it might be a glitch or there is hackers or to any players could have access to something there not supposed to
also do you have any admins?
if you have plugins then you can disable xray and no extra plugin needed
if you have paper just go to files then config then paper-world-defaults then there should be anti xray enable it
and put these also under hidden blocks
ancient_debris
nether_quartz_ore
nether_gold_ore
also put netherrack under replacement-blocks
but if you use spigot or other that are not paper then you need plugins and if youre using bedrock then it will no work
still hope this helped