Thank you for your answer.
I did solve the problem by running the analysis on macOS Big Sur 11.3 (where
this installation suggestion was very helpful, thanks for it!).
Do you think it worth to prepare and send you those data for further investigation? I did encounter this problem before, and at that time the solution was to remove one run for that subject (since I had 5 runs for each subject in this data set). I (or maybe other AFNI users) may encounter this problem later too, when I will do some analysis on this server on which I got the error [OS debian 10.8(x86-64), Linux Kernel 4.19.0-9-amd64].
