capsman ping 50% loss

Hi friends, I have CapsMan sys with 10 caps, all with the same 6.41 version
I see a strange problem, if I configure newly bought RB951ui 2hnd router lika a Cap, I have not problem. But if router is not new, if I used it lika a router, for example for 1-2 years, then I configure lika a CAP - watching ping 50% loss-- 1 ping 0ms, 1 ping 100% loss, 1 ping 0ms, 1 ping 100% loss. Before few days it happened to me with SXT routerboard purchased 2016 june. Also happens if it works lika a Wifi PTP bridge AP mode. After 2-3 days pains I found that if I set /interface bridge set protocol-mode=none, SXT wifi bridge works fine, but another Caps works with standard /interface bridge set protocol-mode=rstp. This is obstacle for remote configure - I lose access and I do not know what to do.

It could be a network loop maybe.

I see a lot of network loops at clients with lightning damage on the router, one port on the router would show as running even if there is no cable plugged into it causing a loop.

If capsman detects a probable loop then it downs the interface for a few seconds

I don’t know how and why, but when I create wan port Trunk with 2 or 3 VLANs all works fine. I use only one vlan