@davidcrb Amazing progress, my friend!
I'm just a bit taller then you (1.7m) and I'm now on the 80 Kg mark.
My goal is to get to the same weight you're at high now.
I was going well, coming down all the way from my old 96 Kg but slowed down with the total lockdown we had here on italy (not eve walking outside was allowed, other then for groceries)
Now that I can walk and see the sun again, I started to track my calories once again.
I'm actually surprised to see that you've dropped your weight that fast with 1700 calories a day, as my maintenance is 1800.
As for BMI, it's only a guideline, if you look like you don't have a lot of fat, don't worry too much, this number is more to orient people that don't exercise and therefore don't build a lot of muscle.
On your diet, I would include some good old vegetables and salads there, man, macros are important, but micronutrients are important too. If you won't, never ever eat a vegetable for anything is this world (I've met people like this) then at least suplement with some multivitamin complex or something like that.
Last but not least, when you start your bulking, increase the calories slowly and watch the progress over the weeks. If you just +500 cals like that you might see that you're gaining more fat then you would like.