Hi @VictoireM
It sounds like your Metabase application database might not have enough resources if you have a big instance.
Have a look in this topic, but specifically my comment on getting the table sizes:
Slow card load after upgrade to 0.42.1
It can also be caused by a reverse-proxy hanging on to the request, on save:
https://www.metabase.com/docs/latest/troubleshooting-guide/proxies.html
Difficult to tell with so little information.
Post "Diagnostic Info" from Admin > Troubleshooting.
And resource size of your servers.