Three way switch with intermittent light functionality
The switch likely has nothing to do with it.

Sounds like you need a new ballast. Or in the era of efficient LEDs, possibly a new fixture, if you care to upgrade.

I used to have a dying fluorescent fixture that was highly humidity sensitive - it would start reasonably on dry days, and take minutes or hours on wet days. There's an LED there now ;^) More light, less watts.

The 25v reading may indicate a bad neutral connection somewhere between the switch and the panel. What's the reading between the wires that are at 125 &amp; 25 relative to ground? 100V, 150V or something else? It may also be the result of inductive coupling between wires and a meter that does not load the line much (induced voltage, which would drop to zero if any amount of current were drawn from the wire, but modern meters don't draw much current at all.) Essentially two parallel wires acting as a low-grade transformer.