Tested it on Sierra... not sure if it happens on other macOS versions...
If you open Keka and compress something, the progress bar appears as it should the 1st time... but if you leave Keka open and try to compress another file, the progress bar is missing...
If you try to resize the notification that is supposed to have a progress bar, then the progress bar appears again and everything works fine (it doesn't disappear anymore if you compress more files) until you close Keka...
After you close Keka, then when you try to compress something it will appear again, but when you try to compress some other file, then it's missing again until you resize the notification.
Tested it on Sierra... not sure if it happens on other macOS versions...
If you open Keka and compress something, the progress bar appears as it should the 1st time... but if you leave Keka open and try to compress another file, the progress bar is missing...
If you try to resize the notification that is supposed to have a progress bar, then the progress bar appears again and everything works fine (it doesn't disappear anymore if you compress more files) until you close Keka...
After you close Keka, then when you try to compress something it will appear again, but when you try to compress some other file, then it's missing again until you resize the notification.