Attendees had been promised an in-depth review of the proof.

By Thursday morning, the cyber experts hired by Mr. Lindell were raising alarms about the alleged cyber-sabotage of the data.

Phil Waldron, the head of the “red team,” said his team received credible information about a “poison pill” inserted into the data. He did not clarify what specific data the alleged poison pill is targeting and whether it is the specific data being analyzed by the experts in attendance.

Mr. Lindell has said he was approached in early January by multiple people who said they had intercepted network data or “packet captures” in real-time on Election Day. He said this data provides “objective proof” of a cyberattack. He hired a team of experts, who spent months validating the material and organized the symposium to present the evidence.

Leading up to the seminar, Mr. Lindell had displayed a video of scrolling, incomprehensible text, which he claimed were the packet captures he had received — proof, he claimed, of his China hacking theory. The video was featured in his documentary “Absolute 9-0” and was played on loop on screens throughout the convention center during the symposium.