FP3+ shows "Call from Unknown" for all received phone calls

/e/ version: 0.16-20210422111920 (22 April 2021)
Device model(s): FP3+

Summary

All the phone calls that I receive are displayed as "Call from Unknown".

Note that above I say it shows "Unknown" but I don't say that it shows the actual number. If it was showing the number, it would mean that the phone does not have this phone number defined in any of the contacts in the phone. Afaict, "Unknown" would be shown when the caller tries to hide his phone number so the callee does not see it.

Note that we tried to put the SIM card in another phone and it did show the contact name instead of the "Unknown", proving that the callee didn't hide his phone number.

Note that randomly it does show the contact name (for the same caller!). We tried to switch off the phone, remove the sim card, move the sim card to another phone and it only showed the contact name once. And we were not able to replicate...

The problem

Use another phone that does not hide his phone number
Call the FP3+ phone with this other phone
The FP3+ does not show any phone number or contact name. It shows "Call from Unknown"

What is the current behavior?

The phone shows "Call from Unknown".

What is the expected correct behavior?

The phone shows "Call from 12345678" (if not in the contact list) or "Call from FirstName LastName" (if in the contact list)