Why unstable VPN connection between Mikrotik and Keenetik?

Question

VPN

Hello.
Mikrotik connects to the VPN server, which is the Keenetik router.
They connect via PPTP.
Every 5 or 10 minutes there is a disconnection, which is immediately restored.
What could be the problem?
Through the same provider, Mikrotik is also a VPN client of another Mikrotik and the connection between Mikrotiks is stable.
Other non-Mikrotik clients also connect to the vpn server on Keenetik and they do not have such a problem.
At the same time, with encryption enabled on Keenetik, Mikrotik cannot connect to it. If you enable the "Allow connection without encryption" setting, then Mikrotik connects to it. The interesting thing is that Mikrotik connects only if you select mschap2 or pap encryption on it, it does not connect at all without encryption, although the connection without encryption is selected on Keenetik.
Moreover, the connection breaks off abruptly, as if Mikrotik on its side decides to restart the connection. Judging by the ping, 2-3 packets are lost in one break.