What you were doing when the issue happened
I pressed the Alfred Hotkey to bring up the search window and typed 'a', 'p' for one of my keywords. The 'a' character went to the application I was using before pressing the hotkey and the 'p' appeared in the search window.
Whether you were able to replicate it a second time by performing the same action
Yes, if 'a' is pressed quickly enough after hitting the hotkey.
Include any screenshots that might help us
Include the Alfred version & build number you are using
4.0.2 [1088]
Include your OS X version
10.14.5