I have "personal" contacts in the RingCentral app (not synced from Google etc). These are often just added from the call history, then I add a company name.
If one of these contacts calls, the company name doesn't show on the inbound call popup (or macOS notification). The company also doesn't show in the Personal contacts list.
On the mobile version of the app, it shows the company name for inbound calls, and in the Personal contacts list, so this seems to be a bug specific to the desktop version.
The work around I've found, is to just put the company name into the Nickname field.
This applies to both the macOS and Windows version.
Version: 126.96.36.1996 Web, 188.8.131.527 Mac
Version: 184.108.40.2066 Web, 220.127.116.117 Windows