More details please about the setup.
Who is clock master, who is clock slave?
At which sample rate are you operating the unit?
To which ADAT port did you connect the expert sleepers, to ADAT1 or ADAT2 of your UFX+?
Firmware version of your UFX+ and driver version.

Post a screenshot of
— UFX+ driver settings and
— Expert Sleepers Control Panel (everything related to clock settings / status and routing).

You could also validate proper operation of ADAT ports at each of the units.
1. configure UFX+ and Expert Sleepers as clock master
2. plug a loop with TOSLINK cable at each of the devices (ADAT OUT to ADAT IN on the same device)
3. validate synch status, post screenshot of UFX+ driver settings and Expert sleepers control panel with clock status.
4. configure expert sleeper again as clock slave, to get clock from ADAT

It could also be worth to test the expert sleeper module in standalone operation (USB disconnected) because then it will have automatically the following settings:
— clock slave (getting clock from ADAT)
— routing analog inputs to ADAT and vice versa
Note: according to the manual, standalone operation requires firmware 1.1.0.
https://www.expert-sleepers.co.uk/es8usermanual.html

It means that when clicking "Channel Layout...", ADAT 9-16 aren't unhide-able, nor are they represented at all.
Despite the corresponding LED showing a connection on the front panel.

Reason I'm not using ADAT 1-8 (which are visible) is bc the flap popped off and the cable will no longer sit secure without sending it off for repair and I need it for a fest I'm playing in a month.

Driver Version:

TM FX Version: