Core callbacks take some time to actually register. Wrap it the call in a pcall, and call it periodically, like the code from this thread`:
local coreCall do
local MAX_RETRIES = 8
local StarterGui = game:GetService('StarterGui')
local RunService = game:GetService('RunService')
function coreCall(method, ...)
local result = {}
for retries = 1, MAX_RETRIES do
result = {pcall(StarterGui[method], StarterGui, ...)}
if result[1] then
break
end
RunService.Stepped:Wait()
end
return unpack(result)
end
end
assert(coreCall('SetCore', 'ResetButtonCallback', false))