wrote
R D S wrote
Phil L wrote

Is there a starter? - 35p each, I'd try this first

Thought the same, done that.

So you've got switchstart fittings. Then it's wrong starters,
bad tubes or bad contacts. The capacitor can't cause this.

Corse it can.

Swapping over to LED won't gain a lot. If it's a series fitting, one fault
somewhere will cause both to misbehave. 2' is likely to be series, 5'
isn't.
Series fittings require 110 starters. For any fitting the starter must
cover the
wattage of the lamp, so no use using a 80-105W starter on a 20W lamp.