The primary node expects a reaction to some packet within a timeframe (this timeframe is adjustable by the --timeout option of drbdsetup). In case the timeout is not met by the other node the primary cuts the connection and tries to reastablish a connection.
In case the other node dies, your primary node will sit there and block all applications which are writing to the DRBD device. Basically it takes the time of the timeout until it desides that the other node is dead. Thus your applications my be blocked for this time.
This is caused when the IO subsystem of the secondary node is slow.
To improve the situation I had the idea of "postpone that deadline" packets. These are sent by the secondary node as soon as it realizes that it will miss the timeout.
Increase the timeout. (Since connect-int and pint-int need to be greater than the timout increase them as well)