I am unsable to break chisel or environmental tech blocks using break block sequence, all of these can be broken with a regular stone pickaxe.

Confirm. Also i can't break obsidian

Not being able to break obsidian is intended.

I'm finding the same thing, but in addition, the CAD can't break vanilla brick blocks, which can be broken with even a wooden pickaxe. This is with the CAD mining level set to the default of 2, though it doesn't seem to work with any mining level.

I'm using the default config setting for the mining level. For some reason, I can mine smoothstone with spells, but not vanilla's chiseled stone bricks.

This problem gets stranger depending on certain factors. Example - If I shoot a circle spell to mine out a huge area of blocks (for example, the first or second spell in this post) and switch a diamond pickaxe into my hand as the spell casts, it's as if the circle's mining level raises to the pickaxe's, and suddenly, I can mine obsidian with the spell. If I switch to a wooden pickaxe, I'm suddenly able to mine the chiseled stone bricks I couldn't mine earlier, but I can't mine iron ore even though I could mine it before. If I switch what I'm holding while the spell is in the middle of being cast, the spell's mining level changes to reflect that. (For example, if I'm aiming at a big patch of obsidian, and switch from a diamond pickaxe to a wooden pickaxe half-way, only half of the obsidian is mined.)

Switching to an empty hand (or a block, or non-pickaxe item) makes the spell unable to break smoothstone, but able to break things like dirt.

I am also having this same issue, from what I can tell the blocks it is not breaking when I look at them with WAILA they don't display a Mining Level. The blocks it is breaking display a mining level in WAILA.
Don't know if that helps, might be a certain way those mods define their mining levels for their blocks. The main ones I have noticed it with are as said in the OP the Environmental Tech blocks and also noticed with the Mekanism ores (Tin, Copper, Osmium).

Though the changes made in revision 40 do help to fix this bug, it's not fixed all the way yet. While CADs are treated as having iron-pick-level mining abilities, there are instances where some spells have buggy mining levels.

Any digging spell that allows the caster to NOT have a CAD in their hand (psimetal tools/armor, circle spell, charge spell, etc.) will change its mining level to match what the player is holding, rather than staying at a constant iron-pickaxe level.

I'm just guessing, but this bug might be related to how mining spells have their mining level changed when they are used in a psimetal pickaxe. If dig spells look at what the caster is holding to determine their mining level (defaulting to iron-pickaxe-level if a CAD is being held), then that may be the source of the bug. Just a guess, though, you know your code better than I would.