big amplitude discrepancy, SA124A

Hello,
I’ve had an SA124A and used it sporadically for a couple years. I find today a huge discrepancy in measured power: a 450MHz sine wave, as measured by my 500MHz BW oscilloscope at 40mv rms, -15dBm, measures +10.5dBm on my SA124A, using default settings, a 25dB discrepancy. In the course of exploring this, I installed the current “Spike” sw, previously I’d used the SignalHound software, but both show similar numbers.

Exploring farther, I find a -30dBm signal (as measured on the scope) measures differently depending on the SA124 reference level:
ref level power at 450MHz
0dBm -14.1dBm
10dBm -4.5dBm

Any suggestions?

Thanks

Rick