Yeah, its not a nute deficiency, its nute burn. I also used to use MG, it seems that MG, since they're just a general fertilizer and not an actual nutrient, tends to just let it slide if we 'accidentally' knock a powdered case of nutes into a container, why? because tomatoes and veggies eat them up... I have grown MJ using MG successfully, but it was in an outdoor garden, using the MG foiler spray that you attach to a hose, and it was more or less an accidental grow.

1/4 strength using MG is WAYYY too strong, and as already been pointed out, even using MG at 1/4 strength you don't have the right compound to flower. I have however used the MG bloom booster which is 10-10-60 (I think) successfully at 1/4 strength during flowering. It is SPECIFICALLY for roses, and did quite well on my cannabis plants for a single grow (didn't use it after)

Good luck bro, everything else looks good!