Hello HomerJ,
I have seen issues like this in the past where the text search was not turned on for all the projects. Text search has two steps in order to work properly. 1) it must be enabled on the DB instance that serves your ALM instances, and 2) it must be enabled for each individual project, just like version control.

I would recommend that you check to ensure the 2 conditions above are met. Since it is working on the other projects then I would say condition 1 was met. You need to address condition 2 now for that one affected project.

I would recommend that you also run a verification on the project and then see also if the project is reporting any issues as it is possible that text search was enabled on the project and has failed due to an issue with the project. The verification is a non-destructive process that can be run with the project active and users in the project working. To run it do the following:

1) log into site admin
2) navigate to the Site Projects tab
3) select the project on the left side (may have to expand the domains to find the projec)
4) right click on the project
5) select the maintenance>verification options
6) select the confirmation operations to run the verification
7) when it completes not the location of the results file completed and note if it says ''verification passed'' or ''verification completed with issues found''

If issue are found then you need to navigate to the results file to find out what the issue is and correct that issue manually if unable to be corrected by the repair process. If it will be repaired by the repair process then schedule a maintenance window to take a back up of the project prior to performing the repair routine as a precaution and then run the repair routine to see if all issues are corrected to include the original one that prompted the verification to be run in the beginning.

Hope this helps and gives something to proceed with,
Dan