Exploring the world while holding a map (scale 3/4) and letting it fill causes the server to severely falling behind until you hold off the map. *Once you stop holding the map, everything is back to normal*. Once you equip the map back, the lag is returning again. This issue has been consistently happening on my server world with this version.

I ran a debug profiling which I attached to this report profile-results-2019-03-03_16.28.02.txt. It appears that while holding the map, *tick.connection* was abnormally leading the tick time and was the reason of the lag, with Rx value bursting up in F3 mode. Eventually this situation was holding the tick for so long that watchdog killed the server. I joined the crash report in case it might help to see the trace / threads positions when the server was stuck crash-2019-03-03_16.30.02-server.txt. (Note: the custom data pack being used is just a bunch of custom functions for counting mobs and is irrelevant to be mentioned here, as it was not even in use during that time, as you can see there is no mention of it in the debug profiling)

Once I stopped holding a map, everything went back to normal, with tps backing up to 20 while exploring.