Well it looks like shedding maybe more of molt. It does seem excessive but every once in awhile rabbits do that.

The absolute best thing is hay, lots of hay – rabbits do not get “hairballs” per se it’s a slow down of the gut that causes a blockage which is why hay, hydration (water or veggies) and activity are the most helpful for this.

Rabbits usually molt 2-3 times a year and sometimes its so mild you may not fully notice while other times it can be a fur explosion. I’m not sure why that is or what makes the difference but out of curiosity has the temperature in your house changed much. Many times molts remain mild as house temps remain stable. I also think the amount of light that changes from summer to winter can be triggers. Is he housed in a different part of the house that is exposed to natural light?

And sometimes I just don’t know why a particular molt is more radical than other Molts…it just is. The fact you see hair growing in seems to indicate a molt rather than a fur issue causes by mites or something else. If this is molt then it should be done in a few weeks.

Encouraging more hay consumption is important and lay off treat during this time to make sure his diet is high in fiber as its the fiber that will help keep the hair moving along in his gi tract. Hydration is very important to so make sure he has access to lots of fresh water as he make drink more if he consumes more hay.

Brushing/combing him more often will help too but be careful not to overdo it or you can create bald spots. Its easy to become ocd with the fur fluffs. Once a day or a few times a week during the molt should be fine.

Looks like a molt to me. Sometimes my buns shed in big chunky patches like that. I suggest brushing every day when they are losing excessive amounts of fur like that.