The most common thing that causes this is the slave is not fully releasing the clutch and it is still dragging slightly so it is hard to shift.
We need to bleed the clutch more just to make sure we have a good pedal. How does the pedal feel? Is firm and feel like you have pressure all through the pedal stroke?
Here is a guide that will help address this:
https://www.2carpros.com/articles/clutch-doesnt-work-sometimes-or-not-at-all
Lastly when you replaced the master did you bench bled it? If not, I suspect you are just pushing and pulling air.
Let's start with this and go from there. I attached the process on how to bleed the clutch in case you need it. Please see below.
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Wednesday, December 16th, 2020 AT 4:24 PM