I’m new to the community but also had this problem with TP Links switches. However in my search of the web and what I did in my home was use only one of the TP Link three way switches. If you use it at the box with the neutral and a regular dumb 3 way at the one with out it should work or at least it has for me. Also even when you flip the switch at the dumb end the TP Link end should register correctly
That’s what I initially did for that light. Though my OCD wants both of them to be a certain way. I actually did all my first floor lights this morning and every single 3way and 2way switches have a Romex of neutrals. So this one 3way is just the oddball I guess. All very weird
What are your plans? I am still very confident on my assumptions above and that you have line and load in the double gang. Should be straight forward to “smarten” up.