Screenshots of pairings and standings: www.smugmug.com/gallery/n-KXMWsD/

It seems like Swiss system tournaments make the matching algorithm go weird once it gets through one cycle of its normal attempt to not match people twice, and will then just match the same players multiple games in a row with no changing it up

Discussed in the Forums in December 2022 / January 2023 here:
boardgamearena.com/forum/viewtopic.php?t=28338

boardgamearena.com/tournament?id=154738
Happened in rounds 14+ of this tournament

I can attest to this issue. I am currently tied at the top of the leaderboard in a tournament that has been ongoing for over three months. This tournament features 3-player Tash-Kalar Deathmatch games. The pairing policy "Try to prevent the same players from being opponents twice" is activated for this event. Despite having played against each participant once, I've found myself repeatedly matched against the same players. My username is superluminal. You can verify the pairings here:

boardgamearena.com/tournament?id=184247

From games 12 to 16 (current game), I've been paired with one player 4 out of the 5 times. Another player has been my opponent in 3 out of these 5 games. Notably, both of these players are at the bottom of the leaderboard. I'm currently sharing the first place with rogernunn1. I fail to understand the logic of pairing players from the top of the leaderboard with those at the bottom, particularly towards the tail end of the tournament. This is the point where top contenders should ideally be pitted against one another to determine the final winner.

Rogernunn1 faces a similar issue. He's been matched with the same player for the fifth consecutive game, a player who seems to have abandoned the tournament and has not done any moves since a long time.

It's deeply frustrating to experience such irregularities, especially after dedicating so much time to a long tournament. I have been desperately waiting for a challenging match against rogernunn1, eager for a good fight. It's only logical that those at the top of the leaderboard should play against one another to determine the ultimate winner. Ideally, players like rogernunn1 and I should be paired, or at the very least, against others with high scores. I suspect that players at the lower end of the leaderboard aren't enjoying this any more than we are, continually finding themselves outmatched by the top contenders.

Another example with the same issue /tournament?id=185083#stage_display

*correct link boardgamearena.com/tournament?id=185083#stage_display

Here's another example. 

boardgamearena.com/tournament?id=249834

Top player matched with bottom 3 for rounds 8&9, and with two of them for rounds 6,7,8,9

Perhaps in the interim, you should caution people not to play more rounds of swiss than floor((total registered -1) / (# of opponents per game)). Or caution that there is a live bug with option ""Try to prevent the same players from being opponents twice"

This is certainly a bug, but responsibility also falls under the tournament organizer for creating such an unconventional Swiss tournament with a high number of matches and very few players, a bad tournament setup IMO. It violates the principles of Swiss tournaments and pushes the code to the edge cases where there will be bugs.

A 20 person Swiss can be completed in 5-6 rounds with a clear winner declared. The ABSOLUTE maximum number of rounds in a 2 player Swiss tournament should be equal to half the number of players, 10 according BGA should actually require a Swiss tournament to have a minimum 2x players per match so minimum 40 players for 20 matches.

If everyone wants to play each other, just use the round robin format up to 15 players and schedule the games apart equal to the game duration so they get 1 game at a time. If you want more than 15 players and a high number of games, just use the Group Stage with round robin format, something like 2 groups of 10 and 5 from each group qualify for finals in a group of 10, that’s 18 matches. Don’t try to use Swiss outside its limits. Just my opinion, I’d prefer BGA devs to focus on improving tournament settings that apply to the existing tournament types for their intended purposes, not edge cases.

This is happening now in boardgamearena.com/tournament?id=346601#stage_display