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Seems like they're just experimenting to get the right amount of raids, or maybe just to reduce lag on the servers. At least this way, players aren't overwhelmed and don't feel the limit of the raid pass.
Not for me since Friday, Sat morning till Mon evening 1 raid. I went for two walks yesterday 2 hours each and not one raid on the 4 gyms. Like everyone else we were seeing at least 2 raids on each gym a day. I put a bug ticket to Niantic yesterday, but trying to contact them is pretty bad.