Hello,
We haven't encountered this issue before.
Did you try to click on the "SecureAPlus Antivirus" at the bottom Windows bar?
Sometimes if there is other window that set to the foreground, the pop-up may be behind the Window. "SecureAPlus AntiVirus" at the bottom bar will keep blinking. This is an indication that the pop-up want to show something, but it can't show it because some other Window prevent it to go the the front. When you click on it, the pop-up should be shown.
May I know what application that you are running when the pop up cannot be shown? Is it Notepad?
As you have suggested, it seems like the Antivirus detected something. Do you know what file that it detected? If the pop-up can't be shown, can you send us the log files, so we can help you to find which file that it detected. Probably it happened on the specific file. If you can send the sample file, may be we can try to reproduce it here, at our side. The details on how to collect the log file can be found at:
https://support.secureaplus.com/how-to-collect-logs/