Well it's going to be obvious if a coin is suspended,

a. no withrawal
b. no deposit
c. no buying
d. no selling

There could be a lot of reasons why a coin is going to be suspended by let's say Binance. But I speculate that it could be of security reasons, maybe there was a hack that is going on or at least that coin has been compromise. So it might take days or months because Binance will resume everything on that coin.