Imo that's probably a calcium deficiency with some K toxicity possibly.
I dont rate canna nutes, never liked em. Biobizz is much better it seems to me..
Possibly your environment is slightly helping the Ca def if the VPD isn't great for chunks of time.
Yup that was my reckoning before, calcium. I still got it when I tried using calcium supplements for it though while I was trying to end it with previous grows. I had it every grow for a year.
At one point I thought it was some sort of fungus so I chucked out and brought brand new everything. Still the same.
Like I say I started using biobizz and stopped mucking around with pH and the spots went away. I wish I had stuck with bb for this grow. Was a big gamble as I had never used canna before.
I'm just working with what was given