The Ducati rider lined up fourth for Saturday’s race before dropping five positions on the opening lap.
He then ran wide at Turn 15 to drop more positions, eventually finishing the race behind team-mate Enea Bastianini as the lowest-running Ducati.
Reigning world champion Bagnaia said he felt like “something was not working well” during the earlier practice session, with the bike “moving a lot”.
He said the team doesn’t yet know what the issue was, but that he was “quite sure” that it didn’t come from his set-up.
Speaking after the race, he said: “Sincerely, my team is already working and trying to understand, checking on the data what happened.
“This morning in the wet I was second in FP2, in qualifying I was fighting for pole position.
“Then already from the warm-up lap I could understand something was not working well, and it was quite difficult to do everything. Riders were overtaking me from the inside, from the outside, and I was a bit on the limit going slow like this.
“It was very difficult but we know our level, we know that 14th is not our position, it’s not our target and we will work for tomorrow.”
Source: Autosport