Same issue occurred on both Safari & WKWebview of iOS 16.0.3 in Oct 2022.
On speicific iPhone models (tested on iPhone 12/13/SE 2020), when "GPU Process DOM Rendering" (previously GPU Process: Canvas Rendering), under [Settings] > [Safari] > [Advanced] > [Experimental Features] is ON, my website ran extremely slow and crashed very often. Also, webfonts, images and icons were not loaded properly. In the meantime, parts of the page blacked out occasionally without reason. However, iPhone XR seems not be affected.
My website: https://hearty.me/hearty
chennien
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I purchased a Cloudflare dedicated SSL ($5/month). And the domain verification passed.