Flole

Well you could run dtdiff on those files and it should list all changes between those 2 versions. If it's only a single change that's it, if there are multiple ones it's a little trial and error to figure out which one caused it.

If you want to investigate further you could decompile the dtb and then compare the 2 dts files to see what changed. It shouldn't be too much I guess.

Using the new kernel with the old dtb's works fine. So the issue is likely part of one of the dtb files.