My experience and discussions with support point to a memory leak that causes this problem. As reported, rebooting the printer in between prints helps with this problem.
The F3 is generally slower than an F2 due to a slow wipe cycle. For Tough 2K, it prints a layer, raises a little, prints another layer, then does a wipe. The build platform pauses for 5-6 seconds before lowering to start the next set of layers. When the memory leak problem starts to show itself the pause increases up to 30-60 seconds per wipe. This results in extremely long print times.
The average layer time for the F2 is about 2 seconds including the wipe compared to 3 seconds for the F3. Currently, even when the F3 is working perfectly, this means the F3 will take 35-50% longer to complete a given print when compared to a F2.