Two stories:

Story 1: There is a HPS lamp in my area that goes for a month or two without cycling but then it cycles repeatedly for two nights, after those nights it doesn't cycle again until a month or two has passed. These times vary from days and weeks and months. These are on your typical magnetic gear that they are usually ran on, the lamps are running for 10 hours a night

Story 2: In my school they have F32T8 CW ALTOs in 4-lamp troffers or Louvres (the cover varies with room). Anyway these lamps can go for a large majority of the school year without having any problems at all but however some do have random screw ups like mercury starvation, striations, swirling, and swirling w/ striations only for it to be back to normal the next time I come back. Maintenance isn't that good either, a whole 4-lamp fixture has to die in order to get replaced, so the lamps can't be getting replaced. But somehow they return back to normal, the lamps all run continuously (I'm talking about hallway lights) for 8-15 hours a day, 15 hours is what they usually get. These are all ran on electronic ballasts

Is there any explanation to why this happens, for both light sources

With the HPS lamp, there are few AEG/Philips Triangel in my neighborhood which have GE Lucalox T 150W which have a similar behavior. They usually don't cycles, but once per month or several months, cycling constantly. One of them located near my hostel: https://www.lighting-gallery.net/gallery/displayimage.php?pos=-141496. When it is cycling, it cycles continuously, sometimes into the night and usually stop after a while, usually early in the morning.
When they don't cycles, they simply vibrates in brightness.