Decode LTE PDSCH messages

I’m trying to decode PDSCH messages by using USRP X310 and srsRAN library.
I successfully decode the DCI and RNTI lists to then use them to decode PDSCH messages.
However, I got a low success rate in the PDSCH messages with high MCS indexes. For example, in the MCS index 27, I only have a 30% success rate, which means among 100 PDSCH messages, I only can decode 30 messages successfully. At the same time, the smartphone such as Note 20 Ultra located at the same location as my USRP X310 still can decode PDSCH messages well with the Retransmission rate is only 10%. The SNR at the experiment position is about 27 dB. I also consider the physical layer configuration of the base station.

I wonder if it is a normal phenomenon or if I got a mistake in my implementation.
Is there any way to improve the success rate?

Thanks for your help.