This is pretty much the same behavior and solution I observed when updating my personal 1260p (FRANGACP06) from 3.03 to 3.06 last year (WD SN850 back then, more RAM, all USB-C expansion cards). Even was the same ReTimer that failed to update. Although, while I am not 100%, I believe I had a different charger plugged in and on the left side back then.
So it seems very much that the ReTimers updating is what is problematic and nothing has changed with that since the 3.06 update. Only that my own FW already had up-to-date ReTimers, so that was not an issue this time around.