Rendered video/image sequences adds frames and sometimes subtracts frames and even seconds (possibly to do with time dilation) UE4.27

Hello! We are having problems with a specific level sequence in UE4.27 (rendering at 30fps). The issue is that the rendered sequence is 2.5 seconds (approx.) longer than the timeline in editor. We realised that we had some time dilation effects on certain shots so we removed those to test the issue and it did help and reduced the rendered duration by 1 second, however we couldn’t figure out why where 1.5 seconds were still coming from. So we started rendering shot by shot and weirdly this resulted in each shot being exactly the correct length when rendered. So, we started rendering chunks of 30 seconds and the issue came back. The render length was slightly longer, but only really in the previously (despite having removed the effect) time dilation affected areas (mostly). However, the main affected area was no longer 2.5 or even 1.5 seconds longer, but 3 seconds and 18 frames shorter! It seems when rendering more than a few shots together this issue starts to occur and any consistent concept of time goes out of the window.

The other less bothering, but still weird problem, is that the rest of the chunks were averaging 4 frames more than the timeline.

We’re out of ideas with this one, but really need to try and get it rendered out ASAP to get the cutscene to the audio department.

We’d appreciate any help. Thank you!