Why are Frames' properties suddenly unable to be set false or true by a script?

I'm coding a page system for a character customization GUI so the user can view every element without them all being on-screen at once. This code immediately comes after I set up the bulk of the system.

for _,f in pairs(tsp:GetChildren()) do
        for _,f2 in pairs(f:GetChildren()) do
            if f.Name == "page1" then
                -- f:GetChildren()[table.find(f:GetChildren(),f2,1)].Name 
                tsc[f2.Name].Visible = true
                tsc[f2.Name].BackgroundTransparency = 0
            else
                tsc[f2.Name].Visible = false
                tsc[f2.Name].BackgroundTransparency = 1
            end
        end
    end

When the script reaches here, I get the error Visible cannot be assigned to at tsc[f2.Name].Visible = false, even though there were no issues at all for months until yesterday. Then hours later, the error occured at tsc[f2.Name].Visible =true, and then an hour later the error went back to occuring at tsc[f2.Name].Visible = false.

The error also only occurs when I set tsc[f2.Name].BackgroundTransparency to 1, but not to 0. There were also no problems with this for months until yesterday.

This is hindering my progress; I saved the script and restarted ROBLOX Studio, I rearranged the code, I even rewrote a simple line to tsc[ f:GetChildren()[table.find(f:GetChildren(),f2,1)].Name ].Visible = true to get the specific name of f2, and the error still occured when set to false, and now when set to true.

Help is greatly appreciated!