What's happening with this autoflowering?

Looks like a trace element issue (boron with the twisted new growth and chlorosis on tips), but probably related to your weird waterign habits as trace elements are rarely physically not present or present in large quantities. Usually it's caused by nute-lockout or pH issues. you say 'up to 600-700mL... this is not how irrigating works. 1) fully saturate pot -- in soilless you also must religiously get 10% runoff waste water - fine to re-use on plants in the earth but not potted plants. 2) wait for appropriate dryback and repeat. Anything else results in dry pockets and potential buildup of nutrients over time in the zones where moisture ebbs and flows depositing minerals over and over in the same spots. Don't overthink it. The volume of water is not something you choose. You give what it takes to saturate the pot - a little runoff is fine in soil too. If you irrigate at a similar dryback, it will take a similar and predictable amount of water - just not of your choice. So, fix the watering habits before doing too much of anything else. since the plant is relatively healthy, otherwise, you can take the patient route for now. Be certain of diagnosis or you'll just exacerbate the problem creating a 2nd problem doing the wrong thing.

I recommend biobizz products, may be more expensive but they are worth it. Say a grower who never ph the water and use botteled drinking water