In the built-in Transmission torrent client, warnings may appear next to the name of the added torrent file. Usually, it is a yellow triangle with an exclamation mark. For example:
If you see such a warning, open the 'Trackers' tab in the lower 'Attribute' panel. Maybe the torrent client failed to connect to one of the trackers for some reason. Usually, in this case, you will see the 'Could not connect to tracker' message.
The reasons for this warning may vary. Still, most often, it appears when the Internet provider filters (blocks) torrents at the DPI (Deep Packet Inspection) systems' level by analyzing the transmitted packets at the transport layer of TCP/UDP protocols. For example, ISP blocks the IP address or domain name of this tracker.
At the same time, you can observe that the downloading of the torrent file continues because, by default, the torrent client supports the DHT (Distributed Hash Table) protocol, which forms a common distributed DHT network between the participants of the file distribution for quick search of peers, which allows you to download the file.
A warning can also mean that there are technical problems on the tracker side, and it is currently unavailable.