I receive "Specify a cache validator" when testing with GTMetrix, why?
Possible causes are:
- Transient issue. The images weren't yet fully processed and because of that they weren't yet cached by the CDN. This usually takes a few seconds and the solution to this problem is to run again the test a couple of times more in the following minutes and this error, in relation to ShortPixel, should disappear.
- Using a different CDN than ShortPixel CDN. Sometimes other CDNs (e.g. Cloudflare) can have settings that will remove the ETag sent by ShortPixel. The solution is to figure out a solution with your CDN provider. For Cloudflare you can read more about when ETag is removed here.
- Low Quality Placeholder. If you see that the URLs of the resources contain the string lqip in the URL, you can safely ignore them. It is a false positive. Those images you see are just low quality placeholders, not the "real images" that you see. This is an example of false positives: