EOS R1 loses focus while using a burst having AF Servo with Flash

[DhandaNot]

I have been using Canon R1 with 600EX-RT for some macro photography of live insects at night which needs the flash. I have set the camera to have slower burst of about 5 shots per second. This allows the flash to work for several shots.

What I notice is that focus is achieved but as the flash happens, the camera loses the focus and then needs time to acquire focus again. Then misses it again on a flash.

As such very few images in the burst are actually in focus. I tried a few times and believe this is a true description of what I am experiencing.

I would like to understand from others if they have done something similar and what was their experience.

I also look forward to comments from Canon Experts.

[deebatman316]

To be fair Brian's signature says "EOS Trainer" but Brian could join in on the flash talks. He is very experienced with flash units and how the EOS R series behaves with flash. Canon made some changes when they switched to the EOS R series.

[DhandaNot]

My Camera is R1 and not 5D Mark iv. The lens is EF (does it matter for the case I am mentioning?) The intermediate images are not in focus.

I typically use a slow speed shoot of sat 5 FPS so that the flash works fine. 

As I said what I have observed is that after the flash I see the subject go out of focus. I am talking about shooting moving insects. I gave example of a Praying Mantis which is moving on the flower / branch.

I use 600EX-RT in TTL mode.