@ernzdl This should give you what you are looking for.
Based on the image below, the regular expression identifies values that contain 2 or more repeated characters. For your use case, you would modify it to identify any values that have 4 repeated consecutive values:
In order to identify the proper rows, we compare the length of the string before and after the regexp and if different (meaning the value has repeated consecutive characters) then flag it as "Invalid"
I hope this helps.