I ran into a similar problem around 12 months ago. Finally managed to pin it down via Resource Monitor. Seems that when the problem occurred there was a service that would max out the activity on my SSD, creating a system bottleneck. Once the offending service was stopped the problem went away.
It may be worth keeping resource monitor open whilst running this character to see if anything similar happens.
I've forgotten the name of the service that caused the issue (sorry).