This is brilliant.I love using RE for solving these kind of kata, but I've never used re.compile before. After reading through the docs again, I can see how simple and beautiful your solution is. You've taught me something incredible today, Thank you!

Best practices? Clever? It’s not a correct solution at all, for example:
arr1 = ['a', 'b', 'b', 'b'], arr2 = ['a', 'a', 'b', 'b'],
this is a test system glitch.

This solution will not pass for :

array1 = ['b', 'b', 'd', 'd', 'c', 'd', 'a', 'b'] and array2 = ['b', 'd', 'a', 'c', 'c', 'c', 'c', 'a']

what

too complicated

check the length of the encoded character, it should be == 8