I play with Ritn-Mods and especially https://mods.factorio.com/mod/RitnGlass.
Game version 1.1.76. All my mods are up to date.
All my LTN supplier stops only process one product.
Core network (-1). No train filter.
My trains systematically look for sand (silica-sand) in stone stations.
I redid all my stone and sand stops.
I also use https://mods.factorio.com/mod/LTN_Combinator_Modernized
I unplugged its modules and replaced them with vanilla constant emitters.
I contacted Ritn who did not find any anomaly that could generate this incident.
The problem reoccurs locally.
Note that I only read and write in English with the help of Google

Thanks for your help