I've been using canna for years and occasionally will do roots org if for veg and they're out of canna. I usually cut it with whatever canna I have left.
I thought it I got a bad batch of canna recently also. I tp all my babes into it and they were fine though so kinda put that to rest. I'm guessing it was my meter being off causing issues. You can only water coco with 6.5 ph for so long before mg and ca issues show up lol.
i chased the problem myself for a couple weeks going through anything that might have changed , meters , nutes , thought my bottle of V/H boost might have gone bad etc ...... everything was just as it should be ..... it all led back to the coco , so i precharged it this time & gave it a good flushing first & the last transplants i did a couple days ago are still looking good . so .......