Slow connectivity on OVPN

Hi. I have a some VPN related problems, maybe someone had something similar.
The router is a CCR1016-12s-1s+ running RouterOS v6.41.2.
Road warriors are using a OpenVPN connection to the main office. Some apps, that connect to local servers, on the remote PC’s are working wary slow and sometimes even drop the connection.
With a PPTP connection to the Mikrotik everything works fine.

UDP-vs-TCP