I've yielded quite a bit in my time as a viking and one thing I've noticed is that resource tiles won't necessarily regenerate in the same area if you tend to babysit and not move from it. Relocate to a new area or send your harvesters on a wee march 

Not a bug though, in my opinion ;)

I would agree with you.

The regeneration of tiles would seem to be more complex than, you clear it, and it comes back pronto in the same spot .

They got to make money from seliing you relocations.

I know that rss tiles are not reappearing in same spot, but usually within few km of one farmed to zero. In this case they didn’t regenerate at all, so after 8 hours farming I’ve used ALL iron rss tiles within 46km radius (only 5 marches, tiles lvl 2). So this IS bug, but I think it was sorted out.