strange gearbox issue

[A500leroy]

2013 combo van

When cold, gearbox works fine
Engine not running, gearbox works fine
When engine gets hot, struggles to get into 1st and reverse( to the extent of switching engine off at junctions to get into gear) and other gears notchy.

Issue?

[gman88667733]

Have you tried changing the gearbox oil? Always an easy and cheap way to start..

[NMNeil]

I'm assuming it's a manual transmission. If so this is an indication of the clutch not disengaging fully.