Nobody else has posted lagginess on the ViX forum. Either a failing storage device as mentioned above or a setting that is corrupt.
Enabling debug log and uploading it will hopefully show the problem. Make sure your IPTV details are not in log. There is a logs menu, the debug logs option and location of both debug logs and crash logs is determined there. You obtain them by FTP.
Edit:
On the other forum, you said you have flashed 6 7 on your Zgemma H7S and there are no issues. You didn't say whether this involved a restore of settings and plugins. Maybe try "latest" again but without restoring settings. The only other thing that could be relevant on the latest image is softcsa code. You didn't say which channels and which softcam.
As an aside, Crash logs will always be generated on VIX. OP has mentioned that he is not experiencing any crashes.