It sounds like your remote is dirty inside. The remote works through a conductive rubber pad, when you push a button a conductive rubber bit of the pad touches a pair of contacts on a small circuit board inside the remote creating a circuit which works the function you pressed. There can be a build up of dirt on the circuit board znd pad which makes the contact z bit hit and miss. There’s an FAQ somewhere on the site telling you how to open the remote and gently clean the board and rubber pad. I usually use a soft nail brush, washing up liquid and warm/hot water on the rubber pad – it must be absolutely dry before reassembly. Isopropanol and a tissue or cotton bud works well on the cuircuit board but don’t wipe the small integrated circuit near one end of the board.

The remote will need a tool to prise the two halves apart and it’s much easier if it’s warm – sunny window ledge works for me.

Failing that it’s a new remote from Humax (Ebay ones may be worse than yours) but I would complain to them directly first, they sent me a new one for my HDR-2000T when it started to fail in the second year from new.