This is pretty common it seems within the Chattanooga city limits since the short term rental district was implemented in 2017 when they passed that ordinance.
I do know that if you were esablished prior to the passing of the new ordinance you are grandfathered in as long as you submit application and ensure you are keeping it current (this is for the city to ensure they can get those taxes!). Outside the zone you can no longer do any short term rental legally speaking period within the city limits. Outside the city limits its fair game currently as long as you have a business license and tax account with the county.
There is an overhaul scheduled for the short term ordinance but that could take a long time moving at city council speed.
I only know this because I have been researching a rental purchase in Chattanooga and have had to answer it for myself. I realize this is 4 months after your question but in case you were still curious or if someone else runs into it hopefully this helps!
Another think to be wary of for those attempting to rent under the citys radar. If you are reported by a neighbor (there is a tattle button on the counties site) and dont cese I think its $25 a day in fines that your are out of compliance or something along those lines.
