All customers with hals, including ourselves, which were upgraded to 8.5 2020-01-07 (build 85330517) experience the same problem, 8.5 2019-11-26 (build 85330317)did not have any problems.
If we turn multithreads off, then it is not possible to run reports in a multi user environment (only one report at a time?), if we turn on, then it is not possible to run exports and maintenances.
We already have "updating web calls while running reports" switched ON.
Previously we had 8.5 2019-11-26 (build 85330317) and did not experience problems with the same hals.