Diy bench power supply snag help

I built this power supply years ago. Its 0-50V and 0-4Amp.
Its been serving me well.
I recently built a mosfet amplifier and decided to test it with my dual bench power supply.
I connected an 8ohm load and 1khz input signal to the amp, and powered it up.
Works great until i reach a certain output level. Then my bench supplies start dropping the voltage and my current limit drops down to 2 Amps from 4 amps.
I did notice that if I bypass the current sense resistor R8 with a piece of wire, the current shoots back up and I regain my full 50v output.
This tells me that there is an issue with the current limit circuit.
I can see a slight oscillation equal to the 1khz fed into the power amp input on the supply rails of my power supply.
I suspect that this is feeding into my current control circuit.
Is there a way to fix this on my circuit??. See attached.
I know its not a fault on my amp board as it powers and works fine on a commercially bought power supply.
Thank you!!

I'd try adding small caps across D1 & D2, and/or D9. Try 0.1uF and see if that has any effect?

I suspect the +/- 10V supply may not be tracking the output fast enough when there is high frequency noise or pulses present.

check C1 with an ESR meter. or increase the size of C1.