Project on LabVIEW 2021 does not work in TestStand 2017

[cpiccoli]

Hello everyone,
Unfortunately, I can't share the code due to company policy, so I'll try to explain myself as clearly as possible.
I have a program developed in LabVIEW 2020 using the DQMH template, exported as an .exe application (with Active X server enabled).

Due to company needs, this program will have to run on a PC with LabVIEW Runtime Engine (not development) 2021 and TestStand 2017 installed.
To use the code on the older version of TestStand without issues, in the PreUUT I launch the .exe and change the adapter by connecting to the ActiveX server of my application.
Some steps (like the classic ShowPanel) work without issues, but others give me the error "(Hex 0x7) File not found," even though the file is indeed present and, before running the test, selecting the "Development" adapter doesn't give me any problems (Note: If I select the runtime engine, it gives me the same error even in the step settings).
However, when I try selecting the VI not as a single file but as part of a project (indicating the project path as well), I get the error "Failed to load VI '....' ... because the VI is broken," even though the VI is not broken and works fine, both when opened individually and within the project.

I have tried following all the steps suggested by TestStand to resolve the issue, tried with and without the project, rebooted the PC, removed and re-added the steps, rebuilt the .exe file, etc., but the issue remains unresolved.

What other tests can I run before I have to rewrite the entire program in LabVIEW 2018? (Something I'd like to avoid since, for example, the project heavily uses maps, which are not available in LabVIEW 2018, and because LabVIEW 2021 is used on the other PCs).

Thanks