Problem uploading Reels

Hello, I have problems with uploading my Reels on IG. Everytime I try to insert the videos for the reels, they don't run smoothly, the stagnate... Also when they are uploaded, they don't run smoothly, there are only pictures, not videos, also my viewers see it like this. What can I do?
Thank you so much for answering

System Configuration: Android / Chrome 91.0.4472.88