Ukraine lost an F-16 fighter jet on Friday morning after an incident on board, though the pilot ejected safely, the Ukrainian air force said in a statement.
“According to preliminary data… an unusual situation arose on board. The pilot moved the aircraft away from the settlement and successfully ejected,” it said on the Telegram messenger.
From what I read, most of these aircraft were at the end of their expected useful life when they were donated to Ukraine.
Throw them into stressful exercise and combat use, with new-to-these-planes maintenance staff, and critical failures should be expected.