Cannot change the volume of tracks, using the default Volume & Pan plugin… – Tracktion Forum

Also never met such errors in TW. As @dysjoint says, this is possible due to automation. Maybe you once had automation recording enabled. If it’s about automation, then if you move the curve, in most cases, in the future, you can change the automated parameters, both with the help of the drawn curve itself, and with the help of the controller in the plugin (there will be no blocking, the blocking will be reset). You can see all the automated parameters through the menu, pointing the cursor at the plugin and opening me with the right mouse button, or using “A” or “+”, transferring them to the plugin automated parameters are colored green. Just play around with these settings.