I have this issue,

I try to check ppl on my queu while queuing mythic plus and once a second person gets in queu i cannot see anyone else queuing, Could someone debug or try to solve this issue please?

5x [string "Error in: Dungeon RIO and Class':'initializ..."]:3: attempt to index global 'RaiderIO' (a nil value)
[string "Error in: Dungeon RIO and Class':'initialization"]:3: in function <[string "Error in: Dungeon RIO and Class':'initializ..."]:1>
[string "Error in: Dungeon RIO and Class':'initialization"]:307: in function <[string "Error in: Dungeon RIO and Class':'initializ..."]:288>
[string "=[C]"]: in function sort'
[string "Error in: Dungeon RIO and Class':'initialization"]:341: in function <[string "Error in: Dungeon RIO and Class':'initializ..."]:281>
[string "=[C]"]: in function LFGListUtil_SortApplicants'
[string "@FrameXML\LFGList.lua"]:1498: in function LFGListApplicationViewer_UpdateResultList'
[string "@FrameXML\LFGList.lua"]:1315: in function onEvent'
[string "@FrameXML\LFGList.lua"]:215: in function <FrameXML\LFGList.lua:136>
[string "=[C]"]: in function RefreshApplicants'
[string "@FrameXML\LFGList.lua"]:1337: in function <FrameXML\LFGList.lua:1336>
[string "=[C]"]: in function Show'
[string "@FrameXML\PVEFrame.lua"]:315: in function `GroupFinderFrame_ShowGroupFrame'
[string "@FrameXML\PVEFrame.lua"]:335: in function <FrameXML\PVEFrame.lua:333>

Locals:
fullname = "Kørpiklaani-Draenor"
score = 0
(temporary) = nil
(temporary) = nil
(temporary) = nil
(temporary) = nil
(temporary) = nil
(temporary) = nil
(temporary) = nil
(temporary) = "attempt to index global 'RaiderIO' (a nil value)"

I realize this is a very old issue, but I just realized going over the issues, that this one is caused by a WeakAura by the name Dungeon RIO and Class and it happened because RaiderIO had some changes that other addons and code had to update on their end to continue functioning properly. I hope you got an updated aura by now and resolved the issue.