Bear in mind 50 watts is not steady state. Average radiated power is likely a watt or two most of the time...but a 20 DB peak is 100 times power....so at a watt average you could well be hitting over 100 watt peaks....
Not a problem with any good amp...many can put out several times rated power for a brief burst...

But crank it to 3 watts average and you are hitting 300 watt peaks...when the amp gets in trouble most think it's the speakers, most of the time it's amp distortion.

Any chain is only as strong as it's weakest link, so I would bet on either bad tuning, as said, or the 50 watt amp just running out of air.