Surfing the web I found this funny site called DeadCoins:
There is a complete list of more than 1000 altcoins which development have stopped or activity frozen by many different reasons.
Also they have as well a classification of SCAM, HACK, PARODY or DECEASED Coins which is interesting to read.
There you can find the summary of why a particular "shitcoin" is considered a "Dead Coin"...
As an example , Zclassic was a coin which a few moths ago reached one of the 50 first positions in the Crypto Coin Market Cap...
The developer Team abandoned ZCL for Bitcoin Private which essentially is almost the same if not equal:
Did you check if you have any Dead Coin in your portfolio?
Enjoy Cryptoland!