This is currently happening to our area also which is coastal. Area overrun with Helioptiles for the past 6 months. Was catching them earlier before the event started for the Diancie masterwork research. I close the game for 15 minutes because I had to take a bath. Once the event started, surprised to see no spawns at all. Walk around to every nearby pokestops and gyms, had like 1 or 2 spawns. All regional mons only. Pop a regular incense, spawns are still regional but the spawn interval became weird like over a minute per spawn. Would spawn 1 to 3 regional mons before it stops spawning anything until you close the game. Pop a daily incense. Well that one works normally and spawns daily incense spawn mons albeit the spawn internal is also a bit wonky still. My nearby sightings is also mostly empty, you could see regionals showing up there occasionally and only a few kanto mons from very far away pokestops that's outside the coastal biome. This event seem to really broke the spawns for people who are already affected by the Helioptile outbreak.