[V8i] ACAD Proxy Boxes?

We have a project that uses a DWG reference. It has been working fine. At the last submittal, last August, this file displayed correctly, showing lines and symbols.

The project has come back up for air, but when I opened the sheet today, I did not see lines and symbols. I just see "Proxy boxes". When I open the DWG file, I see the same thing - all of the boxes "representing" proxy entities.

Our CAD manager is looking into it, but I wanted to ask here. What could have changed over the past six months to make a formerly usable file unusable? I know it's on the MicroStation end because the DWG file in question hasn't been touched since 2016. What has changed in our system so that we can no longer "see" proxy entities? I understand that it may have something to do with object handlers; but we had them before and now they aren't working. Where would we look for the fix to this issue?

Thank you.
Power InRoads