We're running into this issue as well. For us, Chrome users on iOS 15.4.1 can't open phone links that contain the # symbol. Instead, they get a prompt saying "This website is repeatedly trying to open another application". Clicking "Allow" doesn't do anything. The links work fine on iOS 15.3 and older versions of iOS and they also work in Safari in iOS 15.4.1. Encoding the # symbol as %23 doesn't make a difference.

We ran into this same issue on iOS 15.4.1. In our case, tel links that included the # symbol weren't working on Chrome, but they did work in Safari. iOS 15.3 and older don't have the issue. We couldn't fix the issue directly. However, we eventually settled on a less-than-desirable workaround of copying the phone number to the clipboard and instructing users to paste it into their phone app. We also had to specifically detect that the user was using Chrome in iOS so that other users wouldn't be affected. I hope Apple fixes this soon.