This is not a common issue tbh. What sometimes may happen is that after an iOS update the content blockers in Safari becomes corrupted and the only thing that fixes it is not just a reinstall, but uninstall + reboot + reinstall after that. If even this doesn’t help please contact me at “am at adguard.com”, I will try to help.

Thanks for the suggestion! I'll definitely try the uninstall-reboot-reinstall flow. I was about to switch browsers on all the elderly devices.