Did I get this right: This coin does not use plain Argon2, it's a variant with Scrypt-Jane added?
If so, it explains why stratum is rejecting all the found blocks.
This coin would get a great hashrate pointed on the chain if the algo is plain Argon2. To make this clear, I'm gladly hosting a pool if a solution is found for the mining algorithm, stratum implementation of your algo or change the algo.
Yes, LEMON uses Argon2 with Scrypt-Jane. This is same as other "argon2" coins.
I would have actually preferred to use just Argon2, but for compatibility reasons with miner (I didn't wanted to create modified version), I decided to use same POW hash as other coins.
I don't know why blocks submitted by stratum daemon are rejected. LEMON block submission code is exactly same as Dogecoin 1.10. Maybe there are some differences in block format. Other argon2 coins use really old codebase, so looking at code diff is not useful, most lines are different.
I am willing to make changes to LEMON to make this situation better.