So it seems to bs the LGB handset not sending out the signal. I suspect you have an earlier serial handset rather than parallel one.
There are two possibilities:-
I've found my serial handset can play up in this way but as long as you press it once and don't press again until it does it it works. Yours maybe is not reliably sending it.
Or
Your ESU chip has the sounds actually allocated beyond the range of the MTS handset, though then I would have expected the Massoth to have to use the higher numbers. You can move them with the programmer easily but not so easy individually on the MTS handset.
As suggested by Steve above I think LGB's slight deviation from Nmra protocols rear their head when MTS tries to do more than basic control of the loco. Certainly my serial handset equipped MTS runs my locos fine with the cvs set as that post though I would record everything you change so you know what to return it to if it gets worse.
Test after changing every few cv's so you don't go too far wrong. That's where a programmer that can record each profile really helps as going back to the original format is one click away.