Heya,
It's not possible to provide a generic answer to the question.
One would need to know the average line hit rate (average chance of achieving any win based on combination probability, assuming we're talking a typical random slot system).
The reel strip layout would also be needed, given you're talking about 20 line play.
For example, if you had these pieces of information and ran an analysis that yielded, say, a win of some form 1 in every 2 spins on 20 line play, then going 26 spins without a win is astronomical (1/(0.5^26)), or 1 in 67 million and change.
However, if the analysis yielded 1 in every 3 spins (for ease of example), then 26 spins at (1/0.6666667^26)) is 1 in 37877.
Still highly unlikely though.
What system (casino provider) was this on?
Woooof