First of all remember that the app is BETA meaning that the code is being tested.
That is a long-standing premise with respect to BETA installs.
The developer may have simply left in bits and pieces of code that may or may not eventually be removed. Or serving as a placeholder for future plans and actions.
Source:
What link did you use to install the software?
Reinstall - doublecheck that the download is indeed the current and stable version of the software.
And not a BETA version. All too easy with some websites/sources to go astray with respect to finding and downloading software. May or may not be intentional by the "webmasters".
= = = =
That said - other things you can do:
Look in Task Manager > Startup and also look in Task Scheduler.
Most likely some process is either being launched at startup or being triggered later on by some other event or action on your system.
Two other places to look: Reliability History/Monitor and Event Viewer. Either one or both tools may be capturing some error code, warning, or informational event just before or at the time the pop-up appears.
Check all running apps/processes carefully. The culprit may be disguised to look legitimate.
Or may be a legitimate but buggy or corrupted bit of code.
For even more detail use Microsoft's Process Explorer (free).
https://learn.microsoft.com/en-us/sysinternals/downloads/process-explorer
Objective being to discover the culprit and determine if it can indeed be removed/uninstalled or disabled.