The first thing is to make sure that you have followed the network guide. If that doesnt solve the problem you will probably want to contact support. They will need call samples and packet captures, If you can get them. I had the issue with call queues. I dont have it with ring groups.
If they are numbers you don't recognize it might be what I get often at home. The auto-spammer's calling system waits to hear a human voice then there is a long delay before the next available agent actually gets on the call - sometimes nobody ever gets on.
The other point to these calls is that if you answer with a human voice, they know it's a valid line. I've called those numbers back and sometimes get a recording telling me to press 1 for the next operator. SOMETIMES, if you wait long enough, they will say "Press # to be removed from our call list". But if you call one of those numbers back and get a real person, tell them to remove you from their call list or to put you on the do not call list. You may have to threaten with a complaint to the FCC. I've gotten to the point of not answering calls from even local numbers that don't look right to me.
We get a lot of these daily. For a while it was our system not set up correctly on the RC App and customers would call us back, so we knew the call was legit. Nobody calls back now and we've called many of them back and they are always spam. I don't understand why RC can't block them.