I have 2 of these cars. One is a 2015 1.8/auto with transmission problems. Not as bad as yours.
Take it to a small transmission shop for a Dx. They can determine is the problem is either the computer control plate that holds the shift solenoids, or worse: something mechanical that requires a total teardown and new internal parts ($3000).
My mechanic shop told me I needed to pay him $3000 to rebuild my transmission - and he didn't even take anything apart to check. He must have attached his scanner and didn't get fault codes, so by process of elimination: if it's not electronic based, it must be mechanical.
I guess he wasn't about to take out the transmission and tear it apart to tell me the EXACT internal mechanical problem and decided just to rebuild the damn thing and charge me for the price of a factory new unit.
If you are lucky - your problem might be the black plastic transmission control unit with shift solenoids. Less cost. OR - it could even lead back to a bad ECU. Only a scanner pulling fault codes or no fault codes will determine that.
Find a mechanic you trust that doesn't use the CHECK ENGINE light as their personal cash register.
