Maintenance tool has stopped working due to unreachable host

For the past few days to few weeks, the maintenance tool has stopped working. The error seems to be caused by https://mirrors.ustc.edu.cn/ being disconnected. I know for sure it has not worked for at least 4 days, even though it was "fine" around the end of May, when I last successfully used it.

Hosts in China have been an issue with the maintenance tool for as far as I can remember, with extremely poor download performance. See for instance:

• https://bugreports.qt.io/browse/QTBUG-52563
• https://bugreports.qt.io/browse/QTWEBSITE-637
• https://bugreports.qt.io/browse/QTWEBSITE-997

These are only a few of all the issues you could find by using "China" as a search keyword. Most of the time, it is answered as a temporary connection issue or a temporary desync that solves itself.

However, supported by a few years of experience and by the multiple other tasks, I can say connection issues are recurrent and connection speed never was near acceptable, topping in the 100'sKB/sec.

What can I do to connect to a faster more reliable mirror (ideally by picking one myself)?

Thanks.