Happened a few times in T2 for me, about 6-8 weeks ago.

First time, Arkk was invisible for 2 of the 5 people in the party, every other time it was (apparently) just me.

i7-7700HQ, 16GB ram, GTX1060, 512gb ssd (razer blade 2017, specifically)

...with that assumption that has tons of models loading at once on a slow HDD but if it is hardware specific I may still be unable to reproduce it.

You may already have tools for this but if not;

If you can't easily get hold of the hardware, one possible way of testing if it's an asset loading issue on storage with low throughput would be to run it in a VM under QEMU/KVM with gpu passthrough. Have the .dat on a block device and limit IO to that device to different rates to simulate slow/failing storage. Could even use something like NBD+Trickle to add whatever latency you wanted to the storage too, that way you can simulate being that one guy who runs the game from tape storage :)