First time I experienced something like this. Is this a client or a tracker issue?

Might have been debris data (aka peers sending you data that didn't match with the checksum of a file)

Some peers are broken, and keep requesting/offering the same data continuously, probably because of memory or disk errors invalidating the hashes. It is important to check once in a while, and see if there are peers that downloaded more than the size of a torrent, but are still in the same incomplete state. However, receiving bad data should result in temporary disconnect and ignore action from your torrent client.

Some peers may be behind DPI or other network appliance that mangles the data, and need to resend it often. Not sure how it should affect stats.

Some peers may be too slow, so they get dropped, and data is requested from faster peers. However, it shouldn't happen often enough (usually it matters only for the very last segments left to download) to become so noticeable.

There might be a bug in Tixati that makes it discard useful data or count something wrongly.

Without a good close look at your download and its peers, nothing substantial can be said.