I believe simply Alt-Tab'ing out of the game and then re-maximizing it may get it to run at a normal speed.
In the past I had thought that there was an issue with 'process affinity' and multiple-core CPUs. However it appears that my guess may not have been accurate since part of the process of setting affinity involved alt-tab-ing out of the game. If you are curious to see if setting the affinity it makes any difference for you, then you can do so by Alt-Tab'ing out of the game, Ctrl-Alt-Del to 'Start Task Manager' (or however it is now termed with Windows 10). In here go to the 'Processes' tab and find the executable file name for the CM game you're running (such as 'Barbarossa to Berlin.exe', etc.). Right-click on this file name in the list and from the popup menu select 'Set Affinity'. With multi-core CPUs you will have all of the boxes typically checked ('<All Processors>','CPU0', 'CPU1', etc.). UNCHECK ALL of the boxes and then check just ONE of the CPU boxes ('CPU1', etc.). Click 'OK' and then close up the Task Manager and re-maximize your CM game. Again, it appears that simply Alt-Tab'ing out of the game and then re-maximizing it solves the issue, but you can experiment to see if the 'affinity' makes any further difference for you or not.