Why did some of the pictures disappear when moving to https?

Question

Digital certificates

When switching to HTTPS, about 50% of images stopped loading (503 Service Temporarily Unavailable), there were no such problems on HTTP.
There is a script on the site that generates pictures in a cycle, about 100-200 pieces, they weigh a penny no more than 20Kb. They load randomly, at first everything is ok, then part 503, then ok again.
Advise what to do in this case?
Thank you!

Answer 1

50x errors are server errors. In particular, 503 means that the server could not process the request for some reason (for example, it was overloaded).
Look at the web server logs, there should be more details about the cause.