With the P4Pro in video settings PAL 50 fps - and photo settings JPEG - RAW / 3 - 5 burst, the screen/display seems to freeze and turn dark for about 10-12 seconds when taking photographs whilst recording video. When the screen image comes back, I can continue to work. I use Kingston Micro SD 10 XC 1 U3 64 GB cards especially for 4K video. What could be the reason for this delay?

I had same issue. The reason is Dji's poor software. The software is the issue.
You may have to downgrade to the last software version.

I only get a quarter second or so "blink" delay.

Have you tried the scandisk extreme?

Thank you all for your suggestions, much appreciated!
We indeed used to have very short delays, but after recalibrating and upgrading firmware, the problem started to occur.
I will try to downgrade the firmware and use a Scandisk Extreme for 4K.