UI freezing, webcam works in standalone

What is the problem?
UI command window/tab locking up

What did you already try to solve it?
Different browsers, opening webcam in window by itself
Logs (octoprint.log, serial.log or output on terminal tab at a minimum, browser error console if UI issue ... no logs, no support!)
Noting interesting in Octoprint.log. Job started, user logged in
2020-06-11 17:21:05,636 - octoprint.printer.standard.job - INFO - Print job selected - origin: local, path: speednut_0.2mm_PLA_MK3_2h25m.gcode, owner: _api, user: _api
2020-06-11 17:21:05,656 - octoprint.util.comm - INFO - Changing monitoring state from "Operational" to "Starting"
2020-06-11 17:21:05,668 - octoprint.printer.standard.job - INFO - Print job started - origin: local, path: speednut_0.2mm_PLA_MK3_2h25m.gcode, owner: _api, user: _api
2020-06-11 17:21:05,680 - octoprint.util.comm - INFO - M110 detected, setting current line number to 0
2020-06-11 17:21:05,698 - octoprint.util.comm - INFO - Changing monitoring state from "Starting" to "Printing"
2020-06-11 17:21:21,630 - octoprint.server.util.sockjs - INFO - Client connection closed: xx.xx.xx.x1
2020-06-11 17:21:27,917 - octoprint.server.util.sockjs - INFO - New connection from client: xx.xx.xx.x1
2020-06-11 17:21:28,040 - octoprint.server.util.flask - INFO - Passively logging in user userid from xx.xx.xx.x1
2020-06-11 17:21:28,042 - octoprint.access.users - INFO - Logged in user: userid

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ... as much data as possible)
Octoprint version 1.4
cat /etc/octopi_version : 0.17.0
Raspberry Pi 3b+, RPi camera.
Firefox browser 77.0.1 (64-bit)
Windows 7 Pro OS

I'm printing from Prusa Slicer direct to the printer's Octoprint on a Raspberry Pi. RPi is connected via wired ethernet, USB to Prusa MK3s. Prints work fine. The UI is becoming unresponsive though. The video is setup for 720p 15fps. In a seperate browser window [IPaddress]/webcam/?action=stream works fine. Very little lag, maybe a little chppy but I think that's due to 15fps. Back on the UI though, if I access the control tab, the UI freezes. Updates maybe every 20 seconds. If I wait patiently sometimes I can get it to move off the control tab to a different tab. Sometimes it seems to lockup completely. Watching "top -d1" on the Pi, the Pi doesn't seem to be sweating it, reportinging 95% idle. I can start the UI at gcode, watch the gcode fine, and it's OK, move to temperature, still OK, move to the control tab and it goes out to lunch. Appears to be it's video window causing it. Once I've accessed the control tab, subsequently waiting and moving back to the gcode tab, it too is unresponsive, and laggy.

I have no active plugins that I know if. Action command prompt and Bed levelling guide are listed in setup.

Is there some setting I can do to fix this?