Using the new Alpha/Beta version of Sonarr.
I did an interactive search for episode 5 from within the new series and it listed lots of NZBs.
This included:
Magnum.P.I.S01E05.Sudden.Death.1080p.AMZN.WEB-DL.DDP5.1.H.264-NTb-RakuvFIN
Magnum.P.I.S01E05.Sudden.Death.1080p.AMZN.WEB-DL.DDP5.1.H.264-NTb-Scrambled
Magnum.P.I.S01E05.Sudden.Death.1080p.AMZN.WEB-DL.DDP5.1.H.264.1-NTb-Obfuscated
Magnum.P.I.S01E05.Sudden.Death.1080p.AMZN.WEBRip.DDP5.1.x264-NTb-postbot
All of them were flagged as to be ignored by Sonarr due to “wrong series”
Others like these were fine
magnum.p.i.2018.s01e05.1080p.web.x264-tbs-RakuvGEROV
Magnum.P.I.2018.S01E05.1080p.WEB.x264.1-TBS-Obfuscated