Electoral fraud: there are no ballots for my party.
Something as absurd and surreal as what you say can't happen... but it does. Sometimes they hide the party ballots; outside the booth it can be done in different ways: by taking the whole stack of ballots or placing ballots from other parties on top of the stack.
Inside the booth, a more or less similar system is used.
The party representatives and overseers must be alert to this and notify the table presidents so they can resolve it; overseers should never intervene directly.
Another scam option is MAKING YOUR BALLOTS MORE VISIBLE BY LEAVING THEM TOGETHER next to the voting envelopes, or more accessible than the others on the shelves.
2007 - Candidacies without ballots, incomplete tables, and a board member on the lists
"Early in the morning, at the polling station where the mayor of Alicante voted – located on Gerona street – a voter was tirelessly searching without success for the ballots of Ciudadanos-Partido de la Ciudadanía. After asking the table president and a while of protest, the ballots appeared, which were kept in a drawer."