Has this been verified yet?
After all, Iran might not be entirely unbiased in this...
If it does prove correct then lost how?
The Iranians have a navy - two in fact- including as far as known three former Russian attack-submarines. I.e. not missile-carriers but designed to sink other submarines, and surface ships.)
Loss of power on the ship may be by internal fault, of course. She is still "young", commissioned in 2017 with an expected service life of 50 years - unusually long for any ship - but that doesn't mean equipment working almost continually can't break down at only eight and a half years' age.