I think I know why, I was just doing some debugging during your last message.
It seems to be related to another issue related to the index table, it was reported just yesterday. Luckily I have already found a patch, so a quickfix will be available in 2-3 days for sure.
Can you keep 4.26.2 until then? I can suggest a modification for 4.26.3, but it’s going to be patched very soon either way.