I'm not a potter, but I've got a hundred or more bonsai pots, from 100-year old Nakawatari, to two-year old American pots. I've used many over the years. I can say I've never seen glazes leaching off of pots. I have seen glazes change over the years, staining, fading and weathering. I have also had glazes on some Chinese pots delaminate from the clay body and crumble over time. I have also heard second hand that some glazes used by some notable American potters has broken down (as in fell off) in very hot climates when exposed to full sun.
I have steered away from crystalline glazes not only because they're not really useable with tree and a bit faddish (to me), but because I suspect they're not going to hold up over decades of use. Same reason not to use Raku for bonsai pots...
An actual potter will know better though.
Potters may know, but anecdotal reports are definitely of interest! If you're happy to share more info, please feel free to pm me, pictures say a lot.
I know Chinese potters went through a phase of copying old nakawatari but applied glaze thinner and fired at lower temps, to save on cost. I didn't know they would delaminate, or shiver as potters call it.
It's also interesting that modern artisan pots have this issue too. Gutting for everyone, but sharing failures is a good way to avoid it in future.
Crystalline glazes are as safe as any other to the best of my knowledge - oxides want to return to a crystalline state, meaning lots of glazes, like mattes for example, are all crystalline. It's a stable state for the oxide, potters just manipulate it for effect. Some crystal glaze potters fire a pot many times for an effect, but this can weaken a pot considerably. I get that aesthetically it can be distracting.
Raku pots are (normally) inherently weak - the groggy clay is strong but not normally vitreous, and crackle glazes can weaken a pot considerably.
Think I've used enough caveats for a noob now.