I think I'd bleed/replace the clutch fluid and re adjust the slave pushrod setting. You may not have changed the fluid when you did the clutch and the clutch probably needs adjusting now that it is bedded in. Remotely, if the clutch fluid has picked up a lot of water, that water could freeze making the fluid very mushy until it warmed up. If reverse is hard to find, slip it into first before trying reverse. As there is no syncro on reverse this seems to align the cogs and makes selection of reverse easier.