revalidateTag stops working after a few hours in production

[ashKet3]

Summary

I have a route handler that calls revalidateTag when it receives requests. When I first deploy, it works every single time. I can hit the endpoint repeatedly and the cache clears like it should. But after the app runs for a day or so, it starts failing randomly. Maybe 2 out of 5 requests will actually clear the cache, the rest just serve stale data. Nothing changed in my code, same tag strings, everything identical.
The weird part is if I rebuild and redeploy, it works perfectly again for a while, then degrades over time.

Things I've checked

• Tag strings match exactly between fetch and revalidate
• Verified the API endpoint is actually getting hit
• Not seeing this in dev mode, only production

Is there a way to debug this or see logs for what revalidateTag is actually doing? Would help figure out if it's even seeing the tags or if something's corrupted internally.
Also, is this a known issue with long-running production builds? Restarting the process fixes it which makes me think something's getting out of sync in memory.

Additional information

// app/dashboard/page.tsx
async function getData(userId: string) {
  return fetch(apiUrl, {
    next: { tags: [`dashboard-${userId}`] }
  })
}

Revalidation handler:
import { revalidateTag } from 'next/cache'

export async function POST(req: Request) {
  const { userId } = await req.json()
  revalidateTag(`dashboard-${userId}`)
  return Response.json({ ok: true })
}

Example

No response

[snoofox]

is that chatGPT? 😭🙏