Same issue here with Vodafone Germany and the mentioned software update.
Last week I contacted Vodafone and they confirmed me, that the FP3 software update has broke something and that they’re aware of it and working together with Fairphone to resolve the issue.
On Monday (09/13/2021) they called me back to told me, that Fairphone had fixed the unknown caller bug and currently rolling out an update for this. However the new software update has not made it to me. My FP3 still claims it’s up-to-date =/