Sorry to hear that you are facing this issue. The issue you have reported may occur if After effects is not able to get a preview frame in realtime for your Premiere Pro sequence. Usually, this may happen if you are using highly CPU intensive effects like neat video. In such cases, you may either apply such processing-intensive effects at the end if possible or you may try to render and replace the video in Premiere Pro and then send it to After effects as required. Also, you may try to clean the cache in After Effects to check for any issue with cached previews. To do this please go to Edit > Purge > All Memory & Disk Cache. Once done, check the preview.
Hope it helps, let us know if you have any questions.
Sumeet Kumar Choubey