Well I did look into this and found how to fix this... Incase this happens simply go to the Setting of your browser and go to the more tools option ( I have chrome in this case) then click extensions. Once there disable all adblocking extensions then reload aternos.... The thing is if you have the extension enabled and try to disable it from the extension Menu The thing glitches at time by showing the extension is closed but in reality its still open..
If this does not work then go to site settings and search aternos and click on the three dots icon
then click on Aternos.org if it it shows more than one option
Lastly change the following permissions to Allow if they are not already.
if this method doesn't work as well then simply remove the adblocker from your extensions or get a better adblocker that doesn't glitch with Aternos.....
Thats all!