I have several mason buildings around my base and a wall with towers outside. All of those have been converted to stone via the mason buildings. 

However I went on a clust tower spree outside and some of them did not convert despite being in the radius. I have made a tower next to 2 mason buildings that were overlapping, destroyer the tower after 15 minutes and rebuild it. no success.

The other towers awaiting the mason buff did not change either during that time. I did not build walls and they are all stone.

I did teleport somewhere then back

I did relog

I did rebuild mason buildings.

Nothing worked.

Here is a screenshot of a tower overlapped by 3 mason buildings that did not turn despite being placed first and spending almost 20 minutes watching it after I have noticed that nothing else was being upgraded.