M7 Advance Lever Stuck

[Naliny]

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Hello, 

i recently purchased a M7 in “mint” condition from the Leica store in Vienna. I kept on having issues with the advance lever jamming. I sent it back, they couldn’t find anything wrong with it and I have just received it back. 
 

Now I am having the same issue again!!! Before I send it to the store AGAIN i wanted to ask if anyone here might have any ideas of mistakes I might be making? Video too large to attach,  but “on/off button is not the issue. 
The lever is stuck both with and without film! 

 

Many thanks