This is the same as T:ANE. I do it all the time in Trainz-Plus which is the same as TRS22 with more features.
There could be other reasons why things are messed up. In Content Manager, add in all the columns first before doing anything else by right-clicking on the column bar. Once everything is added, resize to fit your screen and move them around where you want them. The reason for this is to make searching and sorting easier because this is helpful for what you need to do.
After setting up Content Manager, change the filter to Open for editing. If there's anything there, select everything by clicking on one asset, right-click and then chose Revert to Original. It could be possible that when you imported old content that something was left open.
Check for missing dependencies.
If your session shows missing assets, right-click on your session, and choose download. This will bring down anything from the DLS that is missing. It won't find old built-in assets though.
Check for asset updates.
Set up a filter:
Click on the small arrow to the left of Filter: to expand the search query.
Click on the plus-sign (+) on the right.
Click where it shows Asset Kuid.
Scroll that list and select Out of Date.
Click the + and change Asset Kuid or whatever is in there this time to Packaged and change that to False.
Save this filter for use later because you'll find it useful to run nearly every day to keep your content up to date.
This will show anything that's installed and available to be updated except built-in or DLC.
Select the assets, right-click and choose download to install the updates.
You can then remove any obsolete assets.
Create a filter as you did above.
Click on Installed.
Add in Obsolete and set to True.
Add in Packaged and set that to False.
This will show any assets that can be deleted.