It is most likely a bug with the MG lobby (yes, another one). It wasn't an issue before, but something they have done, or even a collection of things, has created the problem. I find it steadily gets worse the longer a casino session lasts, which points to some kind of "overflow" in the programme, where a steady build up of "crap" makes the flow steadily less efficient. Simply unloading the lobby software, and restarting the casino from the desktop clears the stuttery spinning, and this points to the program slowly eating up resources as it runs, till Windows has to start making system adjustments to cope, and when Windows is making these adjustments, there can be a brief pause in the foreground programmes that are running. It is not anything I can see even by running the system resources diagnostics alongside the offending MG casino.
In the past, updating MG casinos would rapidly crash Windows with the errors being related to "Windows resources low", and often needed a reboot to fix. This is a clear sign of "crap" being dumped into RAM during the update process, and it never being cleaned up when no longer required, and eventually all the RAM is cluttered up, which causes the resource error, which Windows fixes by expanding use of the paging file, which slows things down even further.