XML File Won't Import

Just to make sure I understand:  A file you exported from Tentacle a week or so ago still imports into premiere?

And you haven't changed anything in your workflow? Updated MacOS or Premiere?  Added a new format media file...?

First, not sure why you're using this software. The website says it synchs a variety of formats... This functionality is built into Premiere.    Besides Premiere, I sometimes use PluralEyes another 3rd party app that will synch a variety of formats...   as every once in a while Premiere will have issues synching...  

An xml file is just a text file that can be opened in a text editor like TextEdit which comes with the mac os.   You could open an old xml which imports successfully and compare it to one of the files that doesn't...  There could be a subtle issue with formatting.  

Another thought, if you have to work with Tentacle (but would be useful for you to explain why you use it).  Download and install the free version of Blackmagic Design's Davinci Resolve (just google it if you don't know where to find it).  Try importing the xml file into Resolve.  If it imports successfully, export an xml from Resolve and see if that file will import into Premiere.  A few years ago I had a client that had started editing in IMovie and wanted to bring that edit into Premiere.  I was able to move the project from IMovie to FCPX.  I then exported an xml from FCPX and that file would not import into Premiere, but if I imported into Resolve and then exported from Resolve it did import into Premiere.  

And finally (actually maybe your first step) would be to reach out to Tentacle support..