http 502 proxy error with browse button after 2 days running

I have to restart archiva every one or two days; if not, archiva becomes unstable :

• main page and admin section are accessible and work fine,
• archiva/browse/ function is dead, giving in navigator :
  Proxy Error
  The proxy server received an invalid response from an upstream server.
  The proxy server could not handle the request /GET /archiva/browse
  <http://archiva.nuxeo.org/archiva/browse>/.
  Reason: Error reading from remote server

Restarting archiva immediately solves the problem.

I didn't find relevant logs, I guess