Doing /fill <coordinates> <block> <dataValue|state> replace <block to replace, ex. minecraft:air> won't work. Here's my command:

/fill 1007 63 1008 993 60 1008 minecraft:chain_command_block 0 replace minecraft:air

It even autocompletes "minecraft:air" for me, but it returns "Data tag parsing failed: Invalid tag encountered, expected '{' as first char."

(If you need me to specify the realm, tell me and I will create a private debug with the realm this isn't working in)
This command works on my private 17w06a server (not exactly the same as up there, but I can still use replace minecraft:air)