ISP identification failing!

Okay, I'm completely stuck and frankly, pretty desperate right now. I launched our web tool, "What is My ISP? - Find Your Internet Service Provider," a while back, and it's been performing great. But for the past couple of days, we're facing critical, show-stopping issues with ISP identification, and I've hit a wall. I need some expert help, fast.

Our tool's purpose is straightforward: it helps users quickly find their Internet Service Provider, their public IP address, and their approximate geographic location. It's designed to be simple, fast, and accurate, with its primary function being robust ISP identification.

The core problem is this: for the past ~48 hours, the tool is consistently returning "Unknown ISP" or wildly inaccurate results for a significant portion of our users. This is directly impacting our primary feature – reliable ISP identification – and essentially breaking the tool's core value proposition.

Here are the symptoms we've observed:

• A high rate of "Unknown ISP" for major, well-known residential providers (e.g., Comcast, AT&T, Vodafone).
• Incorrect ISP names, sometimes showing a datacenter provider (like Google Cloud or AWS) instead of the actual residential ISP.
• Geolocation data seems generally accurate, which is strange, but the ISP data is consistently off.
• We're not seeing any specific error messages in the UI; it's just presenting bad or missing data.

We've already gone through several troubleshooting steps:

• Checked our primary API endpoints (e.g., IP-API.com, and our custom database lookups) – all appear responsive and operational.
• Verified that our internal database updates for IP ranges and ISP data are running correctly and on schedule.
• Cleared cache aggressively on both our server and CDN layers to rule out stale data.
• Tested the tool from a wide variety of VPNs and residential IPs across different regions – the problem persists across the board.
• Reviewed server logs meticulously for any unusual errors, spikes in requests, or API rate limit warnings, but found nothing obvious.
• Cross-referenced results with other popular IP lookup tools; they consistently show the correct ISP, which indicates the issue is on our end, not a global data problem.

At this point, I'm just guessing at potential causes:

• Could it be an issue with a specific IP intelligence provider that's silently failing or feeding us bad data without explicit error codes?
• Is there a common ISP data update or shift in IP block assignments that I might have missed, leading to our database becoming outdated despite regular updates?
• Are we inadvertently hitting some subtle rate limits with an upstream provider that aren't being clearly reported, causing fallback to generic "Unknown ISP" results?

So, my specific questions for this brilliant community are: How do you handle robust and accurate ISP identification for your web tools? Are there common, insidious pitfalls that lead to "Unknown ISP" results that I might be overlooking? Any specific providers, methodologies, or best practices you recommend for maintaining high accuracy in ISP data?

I desperately need expert insights to help diagnose and fix this ASAP. Our tool's core value is at stake, and I'm completely out of ideas. Waiting for an expert reply.