Web Inspector engineer here…
This appears to be a bug in Web Inspector, and we are investigating the issue. Does it happen if you use a recent Safari Technology Preview to inspect your older iOS devices?
In addition to asking on SO.. it is strongly recommended to report bugs pertaining to developer tools at https://feedbackassistant.apple.com/ so that you get notifications about followup questions and when a fix has been shipped.
EDIT(May 14): The issue is fixed in our tree and the fix should be included in Safari Technology Preview 107 and the next major Safari release. Stay tuned for release notes.