Problem with porting an OOT module to 3.8 (sampling speed)

Hello all!
I am trying to port my OOT block to GNU Radio 3.8. It is a source block for my
GNSS frontend. board. The board outputs complex samples with a rate of 16.368
Ms/s. Everything works as expected in GNU Radio 3.7 but after porting the
samples are processed with very low rate (some 16 000 samples per second. This
causes massive overflow in hardware / usb buffer.

I suppose that in 3.8 the source block has to signal required sample rate to
GR runtime. Is this correct?
How to fix the code?

--
Wojciech