I’m not saying that firmware may not be playing a role here but you would be the only report I’ve seen here on this forum with that particular failure mode. The Reddit post you linked to is typical of why I never go on Reddit. I did not see any scientific methodology but I did see a lot of conjecture in that thread.
In the school of trouble shooting 101, there is rule #1, change only one variable at a time. Then there is little practiced rule #2, if a suspect variable cannot be determined, then change any variable one at a time.
So in this case, you’ve decided you don’t want to change any variables, you just want it to work the same way it did before. That’s fair. So the only variable that can be changed under those circumstances is for you to roll back the firmware. Have you tried that?
The other thing that one should be doing with basic trouble shooting measures is simple measurements. Have you tested the temperature of the build plate? To be thorough, and to rule-out or rule-in firmware, you should also do a before and after test temperature test and record your findings on a spreadsheet and repeat the test over a range of bed temps.
The reasons I suggest this testing methodology is that while firmware might seem like the culprit, what if it were the thermistor in the bed sensor that just coincidentally failed too. Yes, I know, I don’t like coincidences either but this should nevertheless be ruled out.
__________________________________________________
I’ve posted elsewhere on this forum but I’ll include it again here. If you don’t already have one, an IR thermometer is way too useful a tool to not have in one’s 3D printer tool box. I put it right up there with nippers and a deburring tool for utility. Also, they are so damned cheap there really isn’t an excuse to not have at least one in the shop. I have a 3 kicking around the shop and home office because I found so many other uses such as troubleshooting faulty electronic components, to car engine diagnostics, to diagnosing my BBQ not to mention both my car and office AC units. I recently had to buy a fourth one because my wife kept stealing mine to use for her cooking. 
When a woman starts stealing one of your tools, that defines “utility”. 
https://www.amazon.com/s?k=ir+thermometer
Another tool that I purchased, originally to diagnose motherboard hotspots for my system building, is a cheap IR imager. Don’t confuse this with a proper FLIR camera, they are not the same. They are quite a bit more expensive than a thermometer at between $70-$120 US but well worth the money for visually seeing where there are thermal issues an a range of troubleshooting scenarios where temperature may be a factor.
Here’s a post I made on that topic recently with examples of the kind of images that can be made with an MLX90640-based imager.