Why it matters
Fingerprinted files never change, so anything short of a year-long immutable cache makes repeat visitors re-download them.
How to fix it
Serve content-hashed assets with Cache-Control: public, max-age=31536000, immutable. Keep HTML on no-cache or a short CDN s-maxage.
Example
Cache-Control: public, max-age=31536000, immutableMore performance rules
void perf reports 25 rules in this category. Core Web Vitals and bytes: LCP, CLS, TBT, TTFB, JavaScript, CSS, fonts, images, caching and compression, measured as the median of several runs on a throttled mobile and a desktop profile.
image-legacy-formatImage served in a legacy formatimages-missing-dimensionsImages without width/height or aspect-ratiorender-blockingRender-blocking resources delay first paintno-text-compressionText resources are served uncompressedthird-party-heavyHeavy third-party footprintdom-sizeDOM is very largebfcache-blockedPage is not eligible for the back/forward cachelighthouse-score-lowLighthouse performance score is low