I have the same problem with Ryzen Mater and Aida64 with same system spec Asus Dark Hero + 5900X.
I was playing with AIDA 64 sensor panel and the temperature varies between what sensor you chose to display. If you select "CPU" in AIDA, on Idle, the temp between Ryzen Mater and AIDA64 are the same, but on full load it's that +10 degrees difference in Ryzen Master vs AIDA64.
If in AIDA64 you select CPU Diode to display temperature form (or CPU Package), on Idle Ryzen Master will show 10 degrees lower (in my case 38C) while Aida64 shows 48C..but on full load they will both shows same temperature...
So yes, this is strange for me also and i'm not quite sure what sensor to display in AIDA64 to be consistent with Ryzen Mater on both Idle and Load...