Urgent help,FCP X keep freezing importing AVCHD

I use the same two Panasonic camera's each year to edit an end of year show for my wife school, but either Hi Sierra o the FCP update has stopped FCP working with the camera's, the video is black and if I try and play it FCP freezes, I've tried to import it three times, if I don't touch it, it imports but if I play it or drag it to a timeline it hangs.It crashes and I see no clips. I've reset the caches and libraries everything. I presume it's missing some kind of codec. I've never had problem with it before.

I've reset preferences, reinstalled FCPX, can anyone help? I supposed to film the second night in a an hour and can't get the dame video off the camera's.
I'm using 2012 Mac Pro Dual 6 core , 32gb Ram, running 10.13.6..

AVCHD footage, or H.264? I'm a gonna a guess a AVCHD codec. You may have to optimize the stuff first. What camera specifically?

I'm on a 2013 rMBP with the latest versions of FCPX and Mojave, I use some AVCHD from GH4 cameras just fine. I still much prefer the H.264 clips out of them, easier to deal with.

What are the specs of the drive you're working off of? If it's the system drive, get fast external storage for your media and Libraries. Also make sure your system drive has more than 15% of its total capacity left as free space.