Attached is the crash log for this. Crashes when pondering the multiblock diesel generator, and only the part when it attaches multiple generators to the back of the first one.

crash-2023-07-19_15.01.55-client.txt

yup I get the same thing on the latest release (1.20)

same issue but my log is a bit different, version 1.20.1-1.1b
crash-2023-07-20_08.58.41-client.txt
it seems some info is also present in logs, although only in the last few lines.

the bug will be fixed in next update in a few days, it's just a simple NullPointerException