What causes a "stuck block" 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?
A few elements of answer:


Difficulty readjustment can be done for each block on some altcoins.
Mining is a highly random process, if you keep on flipping a coin all day, you will get long series of faces. Similarly, the miners may get unlucky. Even in bitcoin you see gaps of over an hour.
The above is compounded for altcoins as miners switch from one to another depending on profitability.


So nothing really unusual. As for a fix, bitcoins' testnet uses a rule where difficulty drops to 1 when no block has been found for 20 min. But the security implications should be thought through.