Is it so difficult to understand? Is it just autocorrect, or a case of pressing the first one that comes up, or do many, many people not know?
If you are shortening 'you are' then it's YOU'RE. The apostrophe is there to indicate the missing letter. For example, 'when you're going shopping, remember to take a bag.'
If 'you are' would not make sense, then it's YOUR. For example, 'take your umbrella if it's raining.'
I can't bear seeing it misued so often. 