I wasn't able to reproduce your issue. When using ScriptPlayer v1.1.1 and also the latest ScriptPlayer beta, the scripts are playing fine on my system. The timeline moves continuously, seeks work, and play/pause also works. I wonder if there's some connectivity issue causing the problem.
How have you set up the timestamp server in HereSphere? I recommend pressing the button next to the HereSphere timestamp server IP to get the local IP address of your Quest 2. Input that into the ScriptPlayer DeoVR IP, with the port appended after the colon. Restart ScriptPlayer after changing the IP. If necessary, add your script folder to the ScriptPlayer Path settings (if using XBVR, you'll need to also download your scripts from XBVR to get the correct title). Then enable the DeoVR player in ScriptPlayer, and it should work, at least it does on my setup.
If it still doesn't work, can you provide more info about how you're playing the video? Like, is it a local file, SMB, or XBVR? Does it happen with all your videos/scripts? Is the video duration in ScriptPlayer correct?