Discord's term of "Synced" isn't to same as the synchronization that TempVoice is doing.
Since TempVoice has the option to lock/open & hide your temporary channel, the permission "view channel" for @ everyone or your access roles isn't synced from the category.
Though other permissions will be synced, but since one permission isn't, it is showing you this hint in Discord.
You have to manually check, if your permissions you wanted to be synced are set.