The EP features five new recordings alongside title track "Diagnosis", which is taken from the band's ninth studio album Renaissance Men, released earlier in 2019.

[2] The EP was promoted on the Renaissance Men Tour Part 2, beginning the day after its release.

[5] Reviewing the EP for Classic Rock magazine, Essi Berelin described Diagnosis as "a second wave of joyous noise" following the release of Renaissance Men earlier in the year.

[6] Berelin noted that the five new tracks are "almost all cut from the same sonic cloth as Renaissance Men, though crushing closer "LOCAC" could easily be a lost effort from Endless, Nameless".

[6] In the same publication's review of Renaissance Men, Neil Jeffries selected "Diagnosis" as the best song on the album.