Either that or traces of Herbicide in the soil?

Wow, that may be the wrinkliest pepper I've ever seen!

All my other in-ground plants are beautiful so I suspect it's calcium deficiency.
I gave them some cal-mag so let's see what happens.

My serrano nearby is loaded with pods and flowers with no bumpiness.

Stoney

(I may be wrong) But I agree with you in that to does appear to be a calcium deficiency.

For my plants ive used the old "smoke master witches brew" with Josh's modification. Basically I put one heaping table spoon of cal carbonate into a jar, slowly add vinegar till it stops reacting... Stir , and microwave. As it heats up you'll notice it reacts more. I add more heat (mircowaving)/cal/vinegar till it smells neutral (like water). Once it smells neutral enough (not like vinegar), and no longer reacting I add 1 tbs of the mix to my waterings .. It's worked out quite well thus far!

And as a bonus, the cal carbonate is dirt cheap on amazon... FAR less than you'll pay for cal-mag. (And if you want the mag, Epsom salt is just as cheap... The white vinegar to react it is likely cheaper than the first ingredients as well;)

...the reaction forms calcium acetate, which is readily available to the plants - unlike the original form (calcium carbonate)

Jay