Is there a cracked tile / shop portal on every level?

Frequently on levels (in all zones) I have encountered a cracked tile, containing a presumably random shop portal (according to the Wiki a shop portal always spawns underneath these tiles). I don't ever remember encountering more than one per level, and as best as I can recall I've encountered it on each level in a zone (i.e. at some point I've encountered it in level 1, 2 and 3 although not necessarily in the same run).

Is a cracked tile / shop portal guaranteed to spawn on each level? My question is specific to All Zones mode, but I presume it functions the same in the story mode.

No, they are not guaranteed to spawn.

I could not find an official source for this. I have found this out by taking the Bard character and digging out literally every wall tile on a few levels. On several occasions, there were no secret portals or cracked walls at all.

Zone 1-1 seems to have a guaranteed secret portal to some shrines, though. Presumably, this is so people can always use the Rhythm Shrine right away.

There are 8 shop portals, each outlined here.

In a given All Zones run, every shop portal appears exactly once. Since there are 12 non-boss levels in an All Zones run, 4 levels won't have shop portals. For example, you will never have two Shrine Shops in a given All Zones run.

Speaking anecdotally, but most of the time level 1-1 contains the Blood Shop. Occasionally it's not, and occasionally there is not shop portal on 1-1 at all. It all depends on the random generation of each level.