@C.Pascal, as far as I am aware, the only mods. from the FE1/FEgold generation that are compatible with FE2 are older aircraft models (for example I run several FE1-era aircraft in FE2). Other mods., such as objects, terrains, etc., are best run in the generation of FE for which they were built. For terrain and other mods. that are suitable for FE2, have a look under this link.
Good terrain mods. that are compatible with FE2 include Caporetto and Caporetto Ver.2, Galicia and Galicia Ver.2, Vosges and Vogesen2, also Italian Terrain. As well compatible are Palestine Terrain (by Stephen1918, not the older Palestine terrain that is available), and North Sea Terrain. As well compatible is the package called First Eagles Seasonal Tiles (by Jan Tuma).
As far as I know, of those custom terrains -- only the package by Jan Tuma includes terrains for several seasons. Obviously, stock terrains in FE2 always include seasonal changes. If you prefer running stock terrains in FE2 to some of the modded terrains, recommended also is the First Eagles Stock Terrains Visual Upgrade (by Stary) -- the upgrade may have been intended for FE1/FEgold but works just as well in FE2.
In terms of visual anomalies such as black terrain tiles, missing tiles, shimmering objects, buildings, etc., recommended is to check over the info. and links in the top half of this post.
Cheers & happy new year,
Von S