I've seen and heard about issues where a coin's network would get 'stuck' at a specific block. I understand why it would get stuck due to high difficulty and low hash, but some coins seem to be unable to mine past a block with low diff and more than enough hash power on the network.
The two examples I can think of are Thorcoin currently stuck at block #85745 and more recently Suncoin at block #180561.
What exactly causes this and how does it get fixed?