does anyone know why certain providers drop off TER periodically.  Does TER drop them or does the provider decide to "take a break".  One in particular has excellent reviews but has been off twice this year.

There are a number of reasons that a provider may be delisted:  fraud, fake reviews, habitual offender, by request, etc.

Sometimes providers request to be delisted due to current family and/or legal situations; once resolved, they may be relisted.