Using an old US POTS phone on OVH SIP

I use an old Western Electric Trimline phone (from the USA) with a CISCO ATA SPA122. The phone sometimes does not ring, it is otherwise working perfectly. However, this phone works ok on my 2 other SIP accounts. Is there any way to diagnose the problem?

There are many many configuration options on the SPA122 (ring voltage, wave form, etc) so I can possibly resolve the problem there.