Hi Ken,
We are under Moodle 3.1.13 (Development -> Purge Caches > Purge All). We are currently thinking of migrating this platform to 3.5 version but it is not so simple ... (because of its size and permanent usage).
Server has 32 GB memory. If I tune php with unlimited memory (cf memory_limit parameter to 0), fatal error also occured ... I think this is a memory leak problem which is probably recent, perhaps because of a recent update of the system packages (kernel or php core).
Thank you for your tips and workaround solutions I will try them as soon as possible.
Cordially,
O.L. (Newbie in Moodle administration)