I'm able to reproduce issues with artist names that include ampersands, I believe it boils down to an inability to parse the musicbrainz response.
Attached is what I believe to be somewhat relevant debugging info comparing macklemore and ryan lewis to m83, although it may be a deeper issue (if the slideshow attempts two lookups for instance)
I'm running latest openelec on kodi
Broken search for Macklemore (checking url, the id is clearly returned)
Code:
1:47:29 T:140318259279616 DEBUG: [Artist Slideshow] the url is: http://www.musicbrainz.org/ws/2/artist?query=artist%3A%22Macklemore+and+Ryan+Lewis%22&fmt=json
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] the params are:
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] {'query': u'artist:"Macklemore and Ryan Lewis"', 'fmt': 'json'}
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] the data are:
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] returning URL as json
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] -----URL OBJECT RETURNED-----
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] {u'count': 1, u'offset': 0, u'artists': [{u'name': u'Macklemore & Ryan Lewis', u'area': {u'sort-name': u'Seattle', u'id': u'10adc6b5-63bf-4b4e-993e-ed83b05c22fc', u'name': u'Seattle'}, u'life-span': {u'ended': None, u'begin': u'2009'}, u'sort-name': u'Macklemore & Lewis, Ryan', u'score': u'100', u'begin-area': {u'sort-name': u'Seattle', u'id': u'10adc6b5-63bf-4b4e-993e-ed83b05c22fc', u'name': u'Seattle'}, u'type': u'Group', u'id': u'97b226c8-7140-4da3-91ac-15e62e131a81'}], u'created': u'2014-12-31T16:41:30.769Z'}
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] playing file is pipe://4/ - Macklemore and Ryan Lewis - Same Love Ft. Mary Lambert
11:47:29 T:140318259279616 DEBUG: Previous line repeats 1 times.
11:47:29 T:140318259279616 DEBUG: [Artist Slideshow] No musicbrainz ID found for Macklemore and Ryan Lewis. writing empty cache file.
for some reason this one works....again checked the json response seems to be aligned.
Code:
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] the url is: http://www.musicbrainz.org/ws/2/artist?query=artist%3A%22M83%22&fmt=json
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] the params are:
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] {'query': u'artist:"M83"', 'fmt': 'json'}
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] the data are:
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] returning URL as json
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] -----URL OBJECT RETURNED-----
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] {u'count': 1, u'offset': 0, u'artists': [{u'name': u'M83', u'area': {u'sort-name': u'France', u'id': u'08310658-51eb-3801-80de-5a0739207115', u'name': u'France'}, u'country': u'FR', u'life-span': {u'ended': None, u'begin': u'2001'}, u'tags': [{u'count': 1, u'name': u'electronic'}, {u'count': 1, u'name': u'shoegaze'}, {u'count': 1, u'name': u'french'}, {u'count': 1, u'name': u'electronic music'}, {u'count': 1, u'name': u'space rock'}, {u'count': 2, u'name': u'dream pop'}, {u'count': 1, u'name': u'synth pop'}, {u'count': 1, u'name': u'dance and electronica'}, {u'count': 1, u'name': u'ambient music'}], u'sort-name': u'M83', u'score': u'100', u'type': u'Group', u'id': u'6d7b7cd4-254b-4c25-83f6-dd20f98ceacd'}], u'created': u'2014-12-31T16:41:30.769Z'}
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] playing file is pipe://7/ - M83 - Raconte-Moi Une Histoire
12:03:41 T:140318259279616 DEBUG: Previous line repeats 1 times.
12:03:41 T:140318259279616 DEBUG: [Artist Slideshow] found a potential musicbrainz ID of 6d7b7cd4-254b-4c25-83f6-dd20f98ceacd for M83