by Ken Task.
Well, you're gonna have to disclose some more info about ... "the reinstallation of additional plugins fails when the web interface is used". Does the attempt return a curl error? If so, does it mention a specific curl error number?
Sounds like you need to leave debugging on and attempt to install a plugin via web interface. Then report what debugging shows ... if anything.
While you are at it, check your server error logs and messages log to see if anything shows there.
Unless you are running a really old and no longer supported version of Linux/Unix OS also mind disclosing that?
'spirit of sharing', Ken