I got that strange behaviour too, at the begining... Don't trust too much "fit" button on surfaces that are non-axial... sometime it works, sometime not, so you have to edit this by yourself...
For "sv_brushmodel NULL": you have an empty entity (an entity that doesn't have any brush), probably a Radiant's bug. You have to either find this entity in your .map file with a text editor... or to restart from a backup of your map (I hope you have backup

), then merging into this backup all the geometry you have done until now (to do it, select brushes in your map, save them as "prefab", open a safe backup, import those prefab into it).
Or if you are lucky: just select the whole map and save it as prefab, start a new map and merge this prefab into it: the empty entity will probably have gone...