Try look at this:

https://forums.veeam.com/servers-workstations-f49/veeam-v9-5-u4-known-issue-veeam-agents-license-t56225.html

Get yourself patched up to 9.5 U4B if you’re gonna stay on 9.5 (though as you’ve said, it’s out of support and you really should upgrade).

Also a couple of thoughts around the license file:

If you replaced the license in the future such as adding capacity, you might find the license is invalid as it was superceded, I’d download the latest version of the license available from your https://my.veeam.com portal, I’d also make sure to get a version in the 9.x format as they changed the license type with 10.

Yes would highly recommend what Michael says about 9.5 U4B patch if you plan to stay but I will say like others highly recommended to upgrade.  If you cannot get the license from your MyVeeam portal then you may need to contact the sales team for assistance.

I know you mentioned using the license from when it was bought, but I just wanted to note that the 9.5 format(s) are different than the v10/v11 format as well, so if you just purchased licensing or renewed and got a renewal license file, that’s going to be in the v10/v11 format and you’ll need to download the older versions from the my.veeam.com portal, or as noted, contact support.  And as others have also said, there’s typically very little reason to stick with such old versions of VBR, although those use cases do exist.