The regex error feature needs a decent npp version.
Afaik 8.2.1 is needed to have the end of line annotation feature.

The real time match update temporarily deletes already styled matches to see what really matches, I hope this makes sense.

Two new ini keys are needed.

; The ID of the style used to display regex errors.
; If there are conflicts with other styles used by Npp or other plugins, change this value.
; The expected range is between 0 and 255; according to Scinitilla.
regex_error_style_id=30
; The color used by the style.
; For an explanation of how this color can be defined, see the following description of the regexes and their colors.
regex_error_color=0x756ce0