1) At the page https://www.zabbix.com/documentation/current/manual/appendix/items/supported_by_platform we can see that vm.memory.size[pavailable] is listed as supported on linux (both). But really it's not. All our servers with linux have 'key is not supported' error in logs.

2) Also we can see proofs just in the documentation:

At

https://www.zabbix.com/documentation/4.0/manual/appendix/items/vm.memory.size_params it's told

"pavailable - inactive + cached + free memory as percentage of 'total'"

and taking back to

https://www.zabbix.com/documentation/current/manual/appendix/items/supported_by_platform we can see that vm.memory.size[inactive] is NOT supported on linux. It's obvious contradiction.