It looks like you did all those basic checks, so I would definitely recommend opening a support ticket for this.
Matthew L. from the Support Team helped resolve this issue. I'm sharing the "fix" so that everyone else can have it - if needed:
Usually when the scans are stuck like that, it has to do with the job engine either being stalled w/ the IPAM jobs or the jobs themselves are stuck. What I recommend doing is replacing the job engine itself to flush the IPAM jobs out and allow them to restart.
Before doing so as well I recommend taking a look at the subnets you have and seeing if an excessively large subnet was added either manually or from a scope as the scanning of such has the potential to cause this.
Replace Job Engine
1. Stop all Orion services from Orion Service Manager.
2. Go to C:\Documents and Settings\All Users\Application Data\SolarWinds\JobEngine\Data\JobEngine35.sdf file and rename it to JobEngine35_OLD.sdf
3. Then create a copy of C:\Documents and Settings\All Users\Application Data\SolarWinds\JobEngine\Data\JobEngine35 - Blank.sdf one and rename it to JobEngine35.sdf.
4. This way you have the old one to revert back to and you always have a blank copy in case issue reoccurs.
5. Right click on properties of the JobEngine35.sdf you have created and untick the read only box and click ok.
6. Restart all Orion Services
Had the same issue today - the above 'fix' also works for IPAM 4.0
The solution works for me too (IPAM 4.0) but - is there some way how to detect this situation (and alert me, of course)? Sometimes it stuck for a few days and I'd like to be informed sooner than my users.
I haven't found a way, to do this (yet) myself.