One possible reason is the movement of hashrate between BTC and BCH depending on profitability.

For example you can take a look at fork.lol and see the big spikes of profitability on both sides....

https://fork.lol/

ok here are a few things you need to know

1- Fork.lol shows only BCH(ABC) hashrate , SV has almost the same hash rate so they in total have about 2 to 3 EH ( which is not minimal at all) at the time of typing this
check it here > https://cash.coin.dance/blocks/hashrate

2- There is a tremendous amount of SHA256 hashing power for rent on places like NH , so that power moves very fast between BTC and other Sha256 based coins, many guys who rent the power use some bots to mine the most profitable coin at any given time.

3-there is a good correlation between price and hashrate, seems like some large farms have their circuit breakers connect to some arduino box that triggers off-on based on price ? no solid proof but very possible , i am aware of farms who cash out btc to fiat like instantly so that they don't take any risk should price fall, so it makes sense to instantly turn off the miners once they are not making enough money to pay for power and bring them back on when the price is up to x.

price



hashrate



notice, price drop on 20th, so does hashrate , price spikes on 22nd so does hashrate. they are not 100% correlated but to a good extend  they are, you can compare them using these sites.

hashrate > https://www.coinwarz.com/network-hashrate-charts/bitcoin-network-hashrate-chart
price > https://www.tradingview.com/symbols/BTCUSD/

there are of course many other factors, but i think these are the strongest.

Other reason is s9 can be change from 13500gh to 9200gh in software in under a minute.

A large miner or two or three could have two power prices.

Low price from 8pm to 8am
High price from 8am to 8pm.

So a guy with 1.35 eh could switch to 920ph

With a auto script it would do the whole farm fast.

Take ten farms and that is a 4.3eh switch