I've experienced the same. Here's a larger collection of obvious spam failing to get flagged by Gmail's spam filters that we gathered: https://www.surgehq.ai/blog/are-the-spammers-winning-failure...

For example, a spammy email that is strangely uncaught:

Subject: ///Y0urFREEFlashlight(NeedYourAddress)///1851

Sender: UBzjwbFb-lyZSC3-noReply@gwhsi.lairpro.com