Importing Players is becoming impossible for me. Please help

so I want to manage a club (no leagues, no matches or stats or tournaments). I simply want to list the players of each category (under 14, under 15, under 17 and so on)

I have created a League for each category (under 14, under 15, under 17 and so on)
I have created the season 2023-2024

I upload my list of teams, OK!
I created the player lists (under 14, under 15, under 17 and so on) and linked to team (under 14, under 15, under 17 and so on)
then if I upload the list of players

Number,Name,Positions,Teams,Leagues,Seasons,Nationality,DoB
1,Joe Allen,Centro,Under 15,Under 15,2023-2024,ita,05/05/83
3,Steven Gerrard,Guardia,Under 15,Under 15,2023-2024,ita,10/03/70
5,Daniel Sturridge,Guardia,Under 15,Under 15,2023-2024,ita,15/02/90
6,Gabrielle Gonzalez,Play,Under 15,Under 15,2023-2024,ita,20/01/87
10,Luca Verdi,Centro,Under 15,Under 15,2023-2024,ita,05/05/83
2,Marco Giallini,Guardia,Under 15,Under 15,2023-2024,ita,10/03/70
32,Stefano Rossi,Guardia,Under 15,Under 15,2023-2024,ita,15/02/90
44,Francesco Airodi,Play,Under 15,Under 15,2023-2024,ita,20/01/87

In the player list they appear linked to more than one Team….

and if I go the under 15 page one player is missing
https://gallotti.org/team/under-15/
Daniel Sturridge is missing but I go to his page
https://gallotti.org/player/daniel-sturridge/
he appers in the team.

this behavior is impossible for me to understand