Curious if what you are seeing is the same as I noted here…
https://forum.mapillary.com/t/sequence-order-issue-2-steps-forward-one-step-backwards/6453
If so I also reported it. Same setup etc. that you describe.
I my case the images appear on the map in the correct order and the connecting lines between points are correct. The problem is stepping through the sequence. I get what I called a 2 steps forward, 1 step backwards effect. The effect only occurs with the reverse, play, forward controls at the top of the screen. Stepping through with the controls overlaid at the bottom of the image seems to work correctly.
A reply in my thread noted similar behavior (sequence taken with a Garmin Virb XE). In that case you could see it in the connecting lines (zig-zagging backwards) between images.
Support contacted me back on this… Last word I got from them was that they were passing in on to their engineering team so that they could examine the issue.
You may want to share a link to the starting image in your sequence (see the sharing icon overlaid on the side of image display) instead of sharing the sequence key. I don’t see an easy way to bring up a sequence with the key. If there is an easy way, let me know.