ConcurrentModificationException in Spring app o - spring

Question

I am trying to run a method to add a score to a player and also add the winner of the match to a list of finalists
The code runs fine for adding the scores, but when I also try and add the winner to the list of finalists, I get the ConcurrentModificationException : null
I have read several posts on this which all mention that they are trying to remove items from a list, but I am not trying to remove anything in this example? Just add the winner.
I have debugged and the first cycle runs fine, but the second time it runs the loop going over the players in the players list, I get the error
public void updateSemiScores(long matchPlayId, String playerOne, String playerTwo, int p1Score, int p2Score) {
//Get the matchplay
Matchplay mp = matchPlayRepo.findMatchplayById(matchPlayId);
//Get the players from this match and set their scores and points accordingly
List<MatchPlayer> players = mp.getSemiFinalists();
//Get list of finalists
List<MatchPlayer> finalistList = mp.getFinalists();
for(MatchPlayer mps : players) {
//If the current player is player 1
if(mps.getMember().getUsername().equals(playerOne)) {
//Set their score as the score for player 1
mps.setSfScore(p1Score);
matchPlayerRepo.save(mps);
//If p1 score if highest
if(p1Score > p2Score) {
//Add the current player to the finalist list
finalistList.add(mps);
//Save the updated finalist list
mp.setFinalists(finalistList);
matchPlayRepo.save(mp);
}
}
//If the current player is player 2
if(mps.getMember().getUsername().equals(playerTwo)) {
//Set their score as the score for player 2
mps.setSfScore(p2Score);
matchPlayerRepo.save(mps);
if(p2Score > p1Score) {
//Add the current player to the finalist list
finalistList.add(mps);
//Save the updated finalist list
mp.setFinalists(finalistList);
matchPlayRepo.save(mp);
}
}
}
}
EDIT
Changing the loop method from for(MatchPlayer mps : players) to for(int i = 0; i < players.size()-1; i++) solves the problem, but I have never come across this before.