Could it have something to do with so-called nice levels? Depending on how and where tasks are run, they are assigned process priority levels and are allocated resources based on that priority level. BTW you can change them interactively by right-clicking a process in Task Manager and selecting "Set priority".
I don't have any other explanation, except that maybe more processes are temporarily fighting for resources by accident when the user is not connected. Try Performance Monitor to figure out what is happening during a realod.
Thanks Peter. Actually there are only 2 levels, but the number of sources is about 50 and they have to process separately until final consolidation. Sources are divided in several groups that running in parallel processes. The next level reload starts after all instances of previous level are finished.
I'll try Perfomance Monitor in two ways, according to your advice. Unfortunately this process runs at late night so it's hard to change priority in Task Manager. I'll try to find a way to set priority for this tasks so they always will start with highest priority level.