The bug

When entering and exiting the game menu, large purple spikes will manifest in the right hand F3+2 graph, accompanied by gaps which would usually be filled in with green. These spikes can often go off the screen (MC-270270).

The presence of these spikes imply that pausing is doing something detrimental to the performance of the internal server, and may be linked to noticeable spikes in client lag at around the same time when pausing.