There is a known issue that sporadically affects iPhone users that disables the click-out functionality on URL links when they are sent in a text message. There is some information in this thread regarding this. Have you by any chance noticed that this only seems to be affecting iPhone users?
Because this is a bug that stems directly from iOS/Apple, unfortunately, there is not too much that we can do to rectify this issue on our end. We have, however, found some information online that you may wish to pass on to your clients when they report the problem:
This is from the following web page:
https://macreports.com/links-from-apps-mail-messages-facebook-etc-wont-open-in-safari-how-to-fix/
Tips on getting URL links to click out correctly on iPhone
Update your iPhone or iPad and make sure that your iPhone or iPad is updated to the latest version of the iOS or iPadOS software
Restart Safari and restart your device
Delete your website data and history Disable JavaScript from within your iPhone settings