Years ago there were other serial interface users looking for a repair to the system at Ignition 7.9, and there should be a colon here yet the forum text editor wants to make an emoji of it...
So you might see if the users with known serial problems earlier have seen it under upgrade, or go to https://support.inductiveautomation.com and either check the knowledgebase, or (if you have not already done so) check the support policies before a voice call or e-mail.. Thanks for telling us what you have seen thus far. Inquiring minds ( and new students ) always wish to know.