Possible bug in GDAL?
My answer to your issue would be to switch to using the Weather-Climate Toolkit from NOAA.
Download Here for Windows/Mac/Linux
It can export gridded and radial NEXRAD/MRMS data to CSV. A sample batch command for anyone needing this assistance would be :
wct-export DataSetName.grib2.gz csv Output.csv wctbatchconfig.xml
If it throws errors, try a different/earlier/beta version of WCT from : https://www1.ncdc.noaa.gov/pub/data/wct/dist/ and be sure to check the sample commands on the website.
As you suggest, this seems to be a bug in GDAL. I tested the same command using GDAL 2.4.2, and it works. The change log for 2.4.0 points to several fixes to the GRIB driver.
GRIB driver:
- replace DataSource? and derived classes with VSILFILE directly for > 4GB file support on Windows
- turn printf() warning as CPLDebug() messages
- read and write missing data values correctly for complex packing when original data is integer (#1063)
- g2clib: avoid int overflow. Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=8194
- g2clib: avoid potential out of bound access (CID 1393528)
- degrib: fix floating point division by zero. Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9407.
- degrib: avoid potential floating point division by zero. Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10291
- add UNIT[] node to SRS on reading, so that is valid