How do i fix my MCreator link problem?

Please help me. I use MCreator link to make a mod with arduino. I have many problems, but the main problem is, that Minecraft doesn´t find my arduino. The first time, minecraft finds it, but if i leave the game without disconnecting, it won´t find it anymore. Also, in the arduino software, my arduino has only errors, so minecraft just destroyed my arduino. I have to use a new arduino in order to test my mod. Can anyone help me fixing this problem? It would be very nice.