This happens when i close the sketch after formatting and saving and when i reopen it it just appears at the top. This time it only appeared in the main tab, but if i recall correctly the last time it happened, it appeared also in other tabs, though i might be wrong there.
I just don’t know what it is there for, and i just deleted it, and it didn’t reappear, while last time i think it reappeared after reopening and i had to do this 2-3 times, though still, might be wrong there 
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Also, i think it only happes when i just used the integrated debugger, so this might be the reason, but even if, i’d like to know what exactly it is there for.
Oh, and this might have something to do with this.
The Debugger sometimes gives errors. Should be able to be replicated by opening the debugger, starting the sketch (not sure if a breakpoint needs to be set too, but i had one), then close the sketch and then the newly opened variable window that is there to debug (or first the window, then the sketch, not sure) and then deactivate debug mode. Once you reactivate debug mode it will give an error and the new window will not appear, but the sketch will run. Then to get the window back, you need to activate the debug mode, start the sketch, end the sketch, end debugmode and when you reactivate it, all is back to normal…
Now i assume this has to do with the debug mode being picky about the window being closed with the x and not by actually deactivating the debug mode… which should be possible to fix…
Edit: I just found the same //<>// like //<>////<>// (literally one after the other) at the top of a secondary tab that never used debugmode (i think… might have accidently activated it before, but not actively) in another sketch.