Recently when I opened Clash of Clans it started downloading content. But it was not downloading so I closed the COC and reopened it but the problem was still there.
So to find the solution I went to google and I found nothing useful and right to solve Coc stuck on downloading content error.
After an hour of struggle found a simple way which you can use to solve this error easily.
The solution is to activate a VPN server only till it completes downloading content after downloading the content you can deactivate VPN and now you can easily enjoy playing Clash of Clans as usual.