This is a relative path to the current mp3 folder. The . at the start means the current folder. Otherwise I don't know what the problem could be. Are the files read-only. Or do the title and the jpg match exactly. Or even the extension for what you think is .jpg is actually a .jpeg.
And for the date use the regular expression action.
... but that is not all ...
... because the tag-field TITLE contains square brackets, which in Mp3tag are characters with special function ...
... we have to outwit the action "Import cover from file" by a format string looking like that ...