IS jerky on EF 400 f4 II with R7

I have had my R7 for almost a month now, and no real issues other than common ones reported by various YouTubers. I use it with the 100-500 RF. However, I just bought a used EF 400 f4 II last week and for the first few days it worked flawlessly. This past Sunday I tried out the EF 2x Teleconverter MK II with this combo. I tried focusing on some distant building and the IS motor went haywire, shaking back and forth for a second, and then it settled out just fine. The salesman said this could happen but it was very disconcerting. I bought the TC anyway and used it for a while that day without issue and took it off and used the lens without it just fine for many hours that day.

Today I was finally able to get enough light to use the TC again. It worked well for birds a few dozen feet away, especially large Great Blue Herons. I just finished editing my birding photos and while I had to use Topaz Sharpen AI quite a bit, it did a decent job. However, shortly after taking the TC off, the IS motor did the same jerking motion, but this time it wouldn't fix itself after a few seconds. I turned the camera on and off and that did solve the problem within a minute or so. 
Has anyone else tried the R7 in combination with this lens and TC yet? Now I am weary of using the TC at all if it's going to cause major IS problems. I had another weird TC experience before. With my R5 and 100-500, after taking the RF 2x TC off, the camera would take a really long time to start up, and sometimes it would just show a blurred image with no icon overlay for up to maybe a minute. I had to pull the battery to fix this. Interestingly the one time I used the 2x + 100-500 on the R7 I had no issues whatsoever.

I have a few more weeks left in my trial period on the used lens, and a bit more time than that to return the teleconverter if need be.

I plan on not using the TC with the 400+R7 over the next few days and make sure the IS issue doesn't happen again. If it does, without using the TC, I will definitely return the lens. I'd rather not as it's really a great lens for lower light situations.

I am pretty sure when removing the TC, I first turned the camera off, and then removed the TC from the lens, then reattached the lens to the camera, which still had the EF-RF adapter on it. Maybe I should have removed the whole lens assembly, including the adapter and TC, from the body, then removed the TC before reattaching to the body? Does it really matter?

Thanks for any advice in advance!

You need version 1.09 firmware on the 400 DO ii lens (not the camera) to work correctly on R series cameras.

https://www.usa.canon.com/support/p/ef-400mm-f/4-do-is-ii-usm

Also version iii (not ii) TCs are best for use on series ii superteles.

I don't have an R7 to test, but 400 DO ii with updated firmware works great on R5 with both version iii TCs.

hstein27 wrote:

IS motor did one jerky motion but quickly recovered. Hopefully this is not a trend.

IBIS has a limited amount of adjustment it can accumulate before it hits the maximum movement sensor is allowed to make. It's not common to hit this in normal photography where your camera movements are expected to be randomized around the same center (it helps if you are trying to hold still while IS tries to help), but if the movements accumulate you can hit a limit where IS has to reset to a new baseline. I hope you just saw that occasional glitch

This reset doesn't always happen. The other choice to make is to fix the sensor at the limit, which is basically an out of bounds scenario where your sensor isn't jumping around, but also means the IBIS has practically switched off or lost its effectiveness. There is probably some algorithmic decision involved to choose when to give you a jerk with continued IBIS and when to detect motion that cannot be effectively stabilized and give up