Thanks for the suggestion. You got me thinking about the dependencies that lead to the source of the problem - the old SRanipal_runtime installation that was not fully removed/overwritten during the update. As I said in my post, we tried the newest SDK available already and the problem persisted. Our target application is actually using the OpenXR which was sufficient for our needs. So we were only SRanipal_runtime dependent and had 80-90 fps just fine. But after the installation of the new Vive Pro Eye software - first, the fps started to radically drop within the first 20s of work of the application. And since the major Steam VR update that got pushed to us yesterday, the eye tracking stopped working altogether.
The problem got resolved with a radical uninstall of everything that is Vive-related up to Steam VR, deleting all leftover files and registry entries, and reinstallation from scratch. I assume SRanipal_runtime of the older version was not correctly removed and the newer version couldn't start up (also it doesn't install in the same location as an old version, so we assumed it's not installed at all), which led us to attempts of reinstallation of the older version with a separate installer.
Consider the following steps to prevent the problem: add a note in the documentation that the new SRanipal_runtime is installed together with Vive Pro Eye software - it is NOT mentioned anywhere. Consider improving the check and cleanup of the older versions of SRanipal_runtime, since there is an obvious and reproducible conflict between the versions.
Thanks again!