Are you amplifying the mic at all? Do you have another receiver that can be used to verify the output of the ubitx?
The only way to be sure is to measure the output. What I have done is build a -50 db tap (My measurements were -45 db actual) to sample the output of the ubitx with an SDR (RSP1A) based spectrum analyzer. If you have an SDR dongle of some sort, there are free SA software packages for them. Here is the -50DB tap that I copied:
I used a two-tone generator built from a kit to drive a BlueTooth speaker with the volume at about what I expected a person speaking to be, and then held the mic at about the expected distance from the speaker. You may also need a step attenuator depending on the power of the amp.
Others have used another receiver with the ubitx connected to a dummy load and the receiver with little or no antenna to lower the input signal. This works best if you have a waterfall display on the receiver. Again, an inexpensive SDR dongle like an RTL-SDR can work.
I would first verify that you do not have any issues with the barefoot ubitx, then go on to the output of the amp. When I did similar measurements for my rigs, I found that it was easy to overdrive both the audio and then the input to the amp. I am currently waiting on a 7 element low pass filter for the amp, as the harmonic output was not within FCC requirements with an eBay 100watt LPF kit that was based on 5 element filters. I also have a -6dp pad in the works to drop the output of the ubitx to below 5 watts.