Repeatedly asked to log in when trying to customise theme

Have you tried:

– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the default theme to rule out any theme-specific problems.

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

.

In that case, I can only suggest that it’s either a server or a local browser issue. Have you tried using another browser?

What about using another computer that’s accessing via a different network/ISP?

In that case, it would seem to be a server issue. I’ve seen similar problems resulting from faulty server configurations, so perhaps you need to speak to your hosts about this.