Recently I've noticed a bug in Codeforces virtual participation. Try running virtual participation for a team contest with the first PC running Windows and the second one running Linux (you may also use an Android phone to reproduce this bug). When trying to register team from the Windows PC, the Linux PC would not show that contest is running and display "Upsolving". The same thing would happen with Windows PC if you register team from Linux PC.

I believe that this could happen due to different ways Linux and Windows store time in hardware clock (RTC). By default, Linux stores global time in RTC, while Windows stores local time. For example, in Moscow Windows PC will have UTC+3 time on its system clock, and Linux will have UTC time. Seems like Codeforces is simply using time on RTC without taking OS in count.

It's not a critical bug, but it makes team participation with both Windows and Linux PCs very inconvenient: you have to send your solution to other PC to send it to judge system. Hope this bug will be noticed and fixed.