It seems like there is a race condition between foreground boosting and probalance where while probalance is still releasing the restraint and setting the priority back to normal that foreground boosting is being overwritten. It requires probalance to be turned off to see the effect of foreground boosting. This applies to both the latest version 16.0.2.10 and the latest beta 16.0.3.1.
This issue is resolved as of v16.0.3.5 BETA.
Note that when a ProBalance restrained process goes to the foreground, you may briefly see it go to Normal before ultimately being elevated to its Foreground Boost setting.
Thanks for reporting the issue and please let me know if you have further feedback.