Error page trashed

Hello,
I get an strange and for the moment unexplained event.
Regularly, every day or often, the personalized page error 404 I created was moved to the trash… Only the main page (in French), not the translated in English.
My configuration :
– WordPress last version
– Theme Pen (free version)
– 404page plugin (work perfectly even this)
– redirection plugin
– yoast plugin
– polylang plugin
And since yesterday to get more information about this trouble :
– WP Activity Log
I get too an Sandbox version of this site on a subdomain to try and test, sorry a staging version.
The default error page was the French version directed by the plugin Error404, the relation translated page in English version never when to the trash.
This morning, I get this message (read on the log of WP Activity Log) :
24/06 10:14:16.088 – ID2012- System – 85.236.157.21 – Deleted – Moved to the trash ID736, Type: Page, statuts published
I read the log of the plugin redirection and I found : nothing detected at this time.
So maybe a maintenance cron made it but I didn’t found it…
I will update this post if I found an issue or if I get more information.
Sorry for my English as I’m French
Thank you for your help
Didier