Calipers could be dirty and need to be stripped and cleaned. Also, sitting for a while after getting wet will lead to rust and sticky brakes. Its not likely the brake master cylinder in my view.
Thank youYou're not losing any fluid of any kind? That kinda removes the master cylinder.
It could be rusty parts, a stone stuck in the caliper. Does the hand brake work?
It can be adjusted with a procedure here- use the search feature for this issue.
Air compressor to clean away any dirt or debris. Maybe some Brake Kleen might help?
Brake hoses ok- no collapsed lines? You could take it to a shop- Midas or the like, lift it up
have them look it over for anything out of the norm. This will involve costs to you however.
Sketchy brakes are not something to take lightly imo. They might seem ok- but the issue
Let us know what happens next if anything pops up again. Your life depends on your
braking system working to the max- just say'n.