As you say the system tray icon brush should flash when it is actually cleaning, and with those settings you should also get a notification when it has finished cleaning.
I suggest the following.
Try disabling Smart Cleaning, close CCleaner, open it again and re-enable Smart Cleaning.
Open a browser and visit a few webpages then close the browser to see if Smart Cleaning runs now.
If not then the next thing to try is to do a 'Restart' of your computer, that's a Restart not a shutdown/boot. (not sure it actually makes that much difference on Win 7 , but it does with 8, 8.1, 10, & 11 so in case someone with one of those is reading).
Do the browser open/close again to see if Smart Cleaning is working now.
If still not then:
Download the 'Slim' installer 'ccsetup578_slim.exe' from here (it's the 3rd one down) and use it to install a new ccleaner over your existing one.
(It should pick up your Pro licence automatically but if not then click on the person icon in CCleaner Free's top right and 'Activate Licence', enter your existing licence key as asked then click 'Activate' - you might want to make a note of your key before starting, just in case).
Do the browser open/close again to see if Smart Cleaning is working now.
Reinstalling over-the-top using the Slim installer can often cure small annoying glitches like this, let us know how it goes.
Usually you can just install the new CCleaner version over the top and it will sort things out.
But as you found sometimes an uninstall and reinstall is needed.
(I'm guessing that the Windows tTask for Smart Cleaner had got corrupted somehow, so it needed to be removed by the uninstall before a new Task was put in place).