Bitcoin's hash rate drop -40%
Bitcoin's total hash rate dropped from 198 million TH/s on Thursday 15th of April to 106 million on Saturday.
Bitcoin's network is programmed to produce around 144 block per day (24h*6blocks/day). Bitcoin network difficulty adjustment happens each 2016 blocks (app. 2 weeks). If hash rate drops rapidly like we are witnessing now, the blocks would be minted slower and 2016 blocks would take longer than 2 weeks before new difficulty adjustment. This could cause transaction fees to skyrocket.
On Thursday 15th of April the number of blocks being produced peaked at 172 blocks, followed by Friday's drop to 103 and Saturday's drop to 91 new blocks being minted. Last difficulty adjustment was on Thursday and difficulty was increased due to high hashrate. If miners don't start soon, we can expect for less blocks being minted and thus higher transaction fees.
In 2017 we had multiple hash rate drops due to China banning cryptocurrencies. When hash rate drops, miners across the world are incentivised to mine after difficulty adjustment.