Why I can see SSID of OTHER P2P link if on that device SSID is hidden...

See picture: Left and right are units with different SSID's. (I write TEST and I hide other SSID's that I saw on location).

MikroTik RouterOS can see it sometimes, but other operating systems will not see it.

hmm... if RouterOS can see that, then it can be added to any other OS %)

Well, hiding a SSID is not a security feature. Anyone with the appropriate knowledge is able to expose a hidden SSID!!

Greetz, Kokel

hidden ssid is not visible immediately, and without extra knowledge you will be see at all. It is good to reduce amount of "accidental" connection count to your AP.