Hello forum, I'm using LRTimelapse 5.5.8, sometimes happens that some of the .xmp files generated by Lightroom after postprocessing the images and saving the metadatas, would not been read by LRT and the preview not uploaded fine. I always solved this problem by uploading the files again or creating new metadata files or start again the entire process of PP. But now I still have the problem. Some of my "wizard keyframes" were uploaded, other images weren't.

What can be the problem?

The main problem is that you are using an outdated version of LRTimelapse which is out of support.
I'd really recommend to upgrade to LRTimelapse 6, which is the maintained and supported version which is also tested to work with the latest OS and Lightroom versions.
If you really, really need to use LRTimelapse 5 because you cannot afford the upgrade, then please install the latest version 5.8, it's on the download page under "Older Versions". But as I said, 6 is the currently supported version.