Uncertain of position is the CAA approved phrase - necessary because they preside over a training syllabus where this occurs frequently, and they cannot openly admit the syllabus is not up to the job of getting around modern airspace.
Lost is the actual outcome.
Oh dear ! uncertain of position can mean both. Uncertain of position and lost.
There was a tragic accident many moons ago where a VFR pilot on top of a solid overcast was uncertain of position.
The poor soul thought he was over the UK but when they traced him his uncertain of position was 200 nm over the north atlantic with no fuel to get back (sadly true)
Uncertain of position means quickly being certain of position by hook or by crook as both are the same.
Pace