As you can see the error says No such file or directory. The qa-page.php file is required almost in every request so if it wasn't there you wouldn't be able to see anything. Now, if you say this is a regular occurance it is weirder because files just are or are not there, there is nothing in the middle. So you should always see the error or never.
So the question you should tackle is actually why the file is sometimes not there to be read. One option would be that you wanted to upload that file (maybe to perform a Q2A upgrade or a core hack) and you first deleted it and then uploaded it, that way the file would have been missing until the upload finishes.
The most likely alternative, IMO, is that there is an issue with the hosting provider. That could be anything, a damaged memory slot, a bad sector on a disk, whatever. I don't think there is much you can do about this but complaining with them. You can explain to them nobody has modified that file and it happens to randomly dissappear (or at least to be unabled to be accessed). If they claim not to detect any issue you can always ask them to move your account to a different server (which will most likely result in a different path to your root (/home/content/28/7343428/).
PS: Based on your Now it's back again I would have to assume you didn't do anything to fix it and it got fixed. Which makes me believe it is more likely that the hosting provider is responsible for that.