Smoothieboard Octoprint 1.3.8 Pause and Cancel randomly don't work

What is the problem?
Pressing pause or cancel will stop the streaming of the gcode, but just hangs the connection. Only solution is to disconnect and reconnect. Problem started with 1.3.8 version of Octoprint

What did you already try to solve it?
Tried upgrading the pyserial version, but made no difference

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)

Smoothieboard 1.1b, Raspberry Pi3, Octoprint 1.3.8

The following is the log. Nothing takes place after the pause or cancel (no more reporting of the state of the printer or temperature or anything). Nothing works other than disconnecting.

Recv: ok
Send: N126454 G1 X212.103 Y160.770 E0.8811*102
Changing monitoring state from "Printing" to "Pausing"
Recv: ok

Known problem with existing workaround:

Sadly wasn't found in the RC (aka: we need more people testing the RCs!)