Inexplicably stops working after a few hours.

I was leaving it mining on my own computers while I slept. I always woke up to the miner not working:

30-01-2018 09:49:06 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:49:16 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:49:26 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:49:36 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:49:46 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:49:56 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:50:06 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:50:16 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:50:26 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:50:36 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:50:46 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:50:56 Miner not running.
wp-monero-miner-util.min.js:1:1141
30-01-2018 09:51:06 Miner not running.

I finally tested it and found out that it just stops working after an hour or so, no matter if it’s FF or Chrome.