After teleporting to another zone Plague Slinger does proc, but stops proccing after a bar swap. Both bars are using Plague slinger weapons.
Swapping back to first bar won't help, the set simply won't proc anymore.
Tested with Class: Nightblade, Race: Orc
Weapon set 1(one hand and shield): Plague slinger Mace, Plague slinger Shield
Weapon set 2(dual wield): Plague slinger Sword, Plague slinger Mace
Plague Slinger belt and rings
PTS server version tested: eso.rc.7.0.4.2236805 2021/05/13 02:38:15 (2100.win.2236938.rc.2236805)
Video of test available upon request.