Vague starting issue

I am having the worst time identifying an issue with my ‘18 Hyundai Kona with 67k miles. Sometimes it turns over extra long before starting. Recently when that happens it will start in limp mode and the downhill assist and traction control lights will come on. Turn car off try again it starts fine. I have had my car scanned at an auto parts store (came up as bad starter), made an appointment at mechanic #1 to replace. They say starter is fine. Battery is 3.5 years old but testing at 83%. Alternator was good. They can’t find a fault, car starts great there and tell me to wait for more symptoms. Car continues to turn over extra (intermittently - worsening at this point - now it starts in limp mode maybe 15% of the time). Visit mechanic #2 to check spark plugs- they pull one say it’s dirty but they don’t think they’re bad. No engine codes coming up for them and the cars check engine light has never come on. They tell me to wait. At this point I’m lost. The car drives great once it’s on. Any ideas on what could be happening? The dealer is my next stop but I’m nervous they’ll tell me it’s nothing too.