It happens all along longitude -8.00000, no matter the latitude
I have long had a set of 3m hgst files for the territory shown, already loaded and with terrtex from Mapbox images. Recently I started laying track on these tiles and i needed to reload the height again. I did it with the exact same hgst files and this started to happen. A few days ago I downloaded a set of 1m resolution hgst files and the same thing keeps happening... therefore I do not thing it has anything to do with the terrain files, but rather with the TSRE5...