@clumsybear Glad that you are enjoying this new process!
I would avoid using png sequences if you can do it with Lottie - png sequences take up a lot of memory if you are not careful.
As for the issues you are experiencing, I have not used drop shadows yet so it might be an issue. You can perhaps try importing to Adobe XD or Illustrator, then to AE, which in theory should be a one to one conversion ( let me know if that works if you do indeed do this ).
I would also test the Bodymovin .JSON output in the HISE rlottie app to make sure it is also translating correctly ( or use this online version http://rlottie.com/)
And to keep an eye on the compatibility list on https://github.com/Samsung/rlottie to make sure you are only using supported features.