Running forever and error 503

I’m having trouble getting it to work properly without breaking my site (giving 503 error).
Most of the times I click generate it stay there forever and does nothing, if I try to open the dashboard in another tab I get the 503 error, and then it’s back, but the error comes back until I go to the plugin and cancel.
Rarely it generates the pages perfectly in under 1 minute. Sometimes it starts and get stuck in the middle.
I’m using WPRocket, I have generated with it activated (more than one time, and the time between 5-10min, but I had to try a lot), I just tried disabling WPRocket and now Simply Static seems to load the ‘generate’ page faster (the log and status).
I’m starting to think that the cache plugin is the culprit, but as I have done with it activated, I’m not so sure.
My question is if there’s known conflict using a cache plugin alongside Simply Static? Is there any minimum server requeriments to run it smoothly? I increased the running time to 100s and WordPress memory to 96mb, the PHP version is 7.4 with 512mb.

Another problem is that sometimes 1 or 2 URL get the 503 error, so I have to redo, I have less than 100 URL, it’s actually a very small site, only aroud 20 pages, the url are the assets and such.

Thank you for your help.