Cheap, cheap switches. Replace them. My 12v light switches have had the same problem after sitting for weeks. I could not find better quality replacements, or even cheap replacements, locally that would fit the fixtures. I looked on the original switches, found the manufacturer part number, googled it, found the exact same cheap replacment on line, and ordered replacements. They should work for a few years and I will do it again.
My 12v light rocker switch under the 5er front overhang did the same thing a few years ago. The switch was not made to be opened to access the contacts, so I sprayed WD40 thru openings on the switch. Has worked fine for several years now. If it starts acting up again, I will just hit it again with WD40. Might even work for the inside light switches.