Lasso tools only using straight lines

Hi there,

I'm going crazy and can't find any solutions on the Internet.

For a couple of weeks now, my lasso tool only selects with straight lines. It's incredibly unpractical.
Pressing Option doesn't change a thing. (I found some advice about doing this to add a straight line to a hand-drawn selection)
It's not using the polygonal lasso symbol when doing so. It's still the basic lasso symbol, but there's a little straight line I never saw before under it. 
I updated the program. I restarted it and my computer multiple times too.

I attached a screenshot of what a round-ish selection looks like.

Does anyone know how to deal with that issue?

Thanks in advance

Laetitia