Buffer underflow error in seepage map

Blood mage in maps.

Unable to reproduce the issue but have some details. I ran seepage the map before with no issues. then suddenly on the next map (which was also seepage) mid way the client crashed with the error message 'buffer underflow'. then when i try to renter the instance, a few seconds later it crashes the client with the same error message. i retried 2 more times to enter, but same error and crash.

next try i enter the map and do nothing. according to the other 3 times, i would have crashed by now. then i walked around for a few more seconds. no issue. then i encounted a pack, killed it (with frostwall + fireball combo). a few seconds later i crash with same error message.

last portal: i will actually count the time
19:12 port in do nothing (longest period of doing nothing vs other crashes)
19:15 start walking around in a circle
19:16 spammed my frostwall + fireball combo
19:17 walked to clear fog, spotted a mob on the corner of screen. few seconds later crashed with same error message.

update: reentered the map and was able to clear it with no issues. so maybe related to instance rather than client side?