Silent fatal error between two batchs

Hello everyone,

Presently, we experiment a weird bug during execution of some batches (but not all).

We should launch a big process on every contents which do corrections. Like we should launch it manually, I create a form which allow to launch batch with the admin interface. By batch, we handle 20 contents (but decrease this number don't fix the bug).

At a moment, the batch stop with only the error:

An AJAX HTTP error occurred.
HTTP Result Code: 502
Debugging information follows.
Path: /fr/batch?id=72&op=do_nojs&op=do
StatusText: error
ResponseText:
502 Server Error
Error: Server Error
The server encountered a temporary error and could not complete your request.Please try again in 30 seconds.

We have no error in logs, no information.

I try to reproduce it on my local (which run with Lando) but we don't have the problem so I can debug it.

I put some debugs messages to see if the problem occurs with specific contents. I added a system to process only contents which haven't been processed to see if I'm able to finish entire batch in multiple time (fortunately, it's the case). It appears the bug occurs at different moment. But these debug messages have allow to see the bug occurs when a batch has finished and the next hasn't begin yet.

We running our website on a gcloud server. The PHP version using is PHP 7.3 (exactly 7.3.12-1+0~20191128.49+debian9~1.gbp24559b), an apache 2 (the version is not inform in the phpinfo) and the Drupal version is 8.8.4