Hi,
I’m guessing that the lcd was working before you removed the touch glass.
The lcd’s are extremely fragile, I recently did a lcd & touchscreen glass on an iPad 9 that had a similar event for someone.
The new lcd that was delivered turned out to be broken (no visible telltale), even though it was packaged safely, so I had to wait for a replacement.
It’s entirely possible that you may have flexed the lcd and broken it when initially lifting up or re- installing.
The only way to confirm is to try another lcd.
Hope this helps