At some point your wallet must have drifted away and created a fork. On this fork your node was alone generating coins that are not spendable on mainnet since your node was alone, staking coins on a fork chain. The rest of the network rejected your blocks and shortly after autoblocked your node that is why you had zero connection.

All the coins your node staked where on a fork chain and not valid on the chain everyone else is on. I find it funny how you did not notice this before since you wrote 13.may 2019 and we are today 26th octrober 2020.

Do take a habit to check your staking node once per week so this doesnt happen again.

PS: Your coins didnt dissapear but you ( your node) was generating blocks on your own fork and those coins are not valid on the chain the current 61 nodes or ony.

This could have happened perhaps for incorrect time on operating system but you really are in charge of your own computer so do check. Set a NTP server to synch your computer time and as said make it a habbit to check your staking node and match the current blockheight with the wallet under help/debug/information (current number of blocks) if its not a match then your node created a fork that no one else follows but your own node. Coin created on that fork are innvalid and unspendable.