Sounds like you have bigger problems than just a break in not going as planned. I can relate, in a way. I've rebuilt about two dozen engines total. Everything from a 125cc honda atv to a 7.2L Cat 3126, as well as cams and bearings on many Mack E7s. One was a 3.6L V6 out of a GMC Acadia. Everything did not go well (fall 2020- winter 2021). By the time I got enough parts and finally was able to test drive it I had the engine out for 4 months. Initial warm ups went great, first couple drives did as well. Then I finally took it over 4,000 rpm and had a catastrophic failure (spun a rod bearing). I still can not figure out what went wrong. Took it all back apart to replace crank, bearings, rings, and do a lot of cleaning. Second go around went perfectly. Sucks, but it is bound to happen. Everyone has a bad day, or some project that doesn't want to go right. Only takes a tiny mistake to become very expensive and time consuming.
All that said, I can tell you how I learned to break in an engine. I had a great Auto Shop teacher in high school until he retired, (the second was very good also). I went to Wyotech for Auto/Diesel technology. The way he taught me was the same as they taught me in college. In college they didn't spend much time on the subject because it is a very small part of Auto Service in reality, but the instructor for the class just happened to do a bit of drag racing as well, and was into the subject more than the curriculum was, and I was interested so we talked further about it. Anyway, best way I was taught was to first wear in cams, then load the rings. Incase anyone found this thread on a search I'll add a guide. This is my own, more in depth guide. So a step by step would be;
1. Pre-lube
2. Start, get oil pressure, shut off, check for leaks.
3. Start, bleed cooling system, run to temp, varying rpm 1,000-2,000 while warming, shut off. Wait 5 min.
4. Start, run to temp at idle, then vary rpm from 1,000-2,000 for 20 min, shut off, wait until cool (overnight).
5. Start, run to temp, drive. Normalish (not only highway or stop and go traffic) driving for a few miles, then check over.
6. Seat the rings by loading. Highest pressures at the lowest rpm you can get. Manual transmission is easy, up shift and put the foot to the floor. Auto is more difficult, you need to load the rings as much as possible without upshifting. Best is to Load for 10-15 seconds at a time, then coast for 15-30 seconds. Repeat for 20-30 minutes. Keep on eye on the temp gauges, full throttle is good, but keep RPM under 2/3 of full (approx 4,000 for gas, 2,500 for small diesel, 1,800 for large diesel). The goal is to get the rings to seat into the cylinder walls, ie knock off the microscopic ridges created while honing the cylinder and create an almost perfectly flat face on the ring to provide a nearly perfect contact between the ring and the cylinder wall. The cylinder wall should have microscopic valley's left to hold a tiny amount of oil to provide enough lubrication to prevent wear without having so much that it is able to burn off during combustion. If I remember correctly the cylinder walls should look like an AC voltage graph cut off at 0 volts, showing flats with valleys that are far too small to hold any debris or enough oil to burn.
7. Do several very short full rpm sweep runs. Most vehicles now break the speed limit in 2nd gear and won't let it get to a high rpm in first. But the idea is to shake out any problems that might occur during a passing run, so do what you can.
8. Change the oil and you're good to go. Recommend changing the oil again after 500-1000 miles of normal driving. Fewer if only in town, longer if only highway.
Rant begin
I've followed this setup on every engine I've done except 2. One really because I wasn't the one that rebuilt it, it was a 115hp evinrude 2 stroke, and I freely admit that me and 2-strokes don't really get along well. Long story shorter, I know my limitations so I purchased a rebuilt boat motor from a marine shop (technically I purchased it from them to be rebuilt by them). They took too long and I saw another motor (nearly identical) very cheap that needed to be rebuilt. I bought that motor, rebuilt it myself over a weekend, for 1/4 the price including rebuilding it. I broke mine in as close to how I'd done every other engine I rebuilt. That was 5 years ago. I still have that motor. It is on a smaller boat that gets 20-40 hours a year on it, with 3/4 of that being as hard of a life as I could think of for a boat motor, all out pulling a tube with teenagers on it. The motor runs perfectly. Better than any 2 stroke I've ever seen. If it weren't for that, I'd have given up on 2-strokes all together 5 years ago. When I finally received the other motor, they had a very specific break in process (and oil) that I had to follow, that was nothing like my usual process. It took it easy for a long (very long) time, such as 2-3 hours at 1,000 rpm, then 2-3 hours at 1,500 rpm, etc. After the break in, that motor went on to my pontoon, which sad to say hasn't been used much since we got the smaller boat. What a waste of money. I bet it has only seen 30 hours since the rebuild 5 years ago. Despite being almost an identical motor, it has been nothing but problems. Some can't be contributed to the person that rebuilt it directly, such as coils going bad, a lower unit leaking, or carbs that need cleaning (he just didn't do a comprehensive rebuild, more of a remanufacture in my mind). But despite that, it has always been really tough to tune and not ever run just right. I don't know if they did a bad job, or the type of break in just wasn't as good. I can tell you that as of a few weeks ago, that engine had 105-115 psi of compression on all 4 cylinders, while the one I rebuilt has 120-130psi of compression. Both technically within specs, but why would a professionally rebuilt boat motor have consistently lower compression than one rebuilt by a Med/Heavy truck tech that probably shouldn't be rebuilding 2 stroke boat motors. While also having about 1/5 the number of hours on it.
Rant end
I've read of many different ways to break in an engine. I've been given instructions for other ways when installing a rebuilt engine (which I've ignored). I do spend a relatively large amount of time breaking in an engine. With the exception of the one, I've never had a problem I still attribute that problem to my ongoing physical and mental problems. I've only rebuilt two for work many years ago because it is cheaper for a shop to get a rebuilt engine and install it, than to rebuild it themselves. Most I've rebuilt were mine, or friends. I still own a few that I've rebuilt, with the most recent being my Wife's duramax. Just passed 2,000 miles and working perfectly. I did an in frame overhaul on my dump truck (7.2L cat) last summer, then hauled 500 yards of gravel to my place with it with no problems. My point is that I've heard of many different ways, in instructions or on the internet. But my adapted way is the closest to the way I was taught, and hasn't failed me yet. No engine that I've rebuilt burns oil or has low compression and I still know the person who has that first ATV that I rebuilt 25 years ago in high school.
