Your FME Form is of a (slightly) newer version (2024.0.1) than your FME Flow (2024.0). Unfortunately this is not supported.
See the last sentence in this quote from FME Versions and Workspace Compatibility:
Publishing from FME Form to FME Flow
Compatibility between FME Form and FME Flow when publishing workspaces is slightly different than compatibility within FME products. For best results, FME Form and FME Flow should match in versions when publishing. However, publishing is supported if the year and major version match and the version of FME Form is the same or older than FME Flow. For example, publishing from FME Form 2024.1.1 to FME Flow 2024.1.2 is supported, but publishing from FME Form 2024.1.3 to FME Flow 2024.1.2 is not supported.
The changelog from version 2024.0 to version 2024.0.1 mentions (among other changes) a change to StringSearcher. This is probably the cause of your problem.
So the solution is to upgrade FME Flow or downgrade FME Form (or upgrade both to the newest version).