Found the word ‘recrudescence’ in the opening paragraph of ‘The Elf Trap’ by Francis Stevens, again from Tales Before Tolkien.
INTRANSITIVE VERB: Inflected forms: re·cru·desced, re·cru·desc·ing, re·cru·desc·es
To break out anew or come into renewed activity, as after a period of quiescence.
ETYMOLOGY: Latin recrūdēscere, to grow raw again : re-, re- + crūdēscere, to get worse (from crūdus, raw).
OTHER FORMS: re‘cru·des’cence —NOUN