Smart Lock issues on FP4

I have an FP4 since about 10 days now and I am pretty satisfied with it. No real issues apart from one: I have activated Smart Lock with my home as safe place and it worked first well for about a day, then did not work for another day or so, then suddenly worked again and now since last night stopped working again. I have not left my home meantime (since I have to stay in because tested + on Covid) - and location services are working well when I am using maps etc. Anybody an idea or a tip about a setting or so that I might have missed?