I've upgraded to GDAL 3.0.4 and libgeotiff 5.0.1 (packages from Ubuntu 18.04 LTS to 20.04 LTS) and all my software that uses OGRSpatialReference to perform coordinate transformation on GeoTIFF data sets is now broken.
Basically when opening a data set (also via gdalinfo)
I get:
proj_create_from_database: prime meridian not found
proj_uom_get_info_from_database: unit of measure not found

I've cloned the latest source and built libgeotiff myself. Now on version 5.1.0 I get only:
proj_uom_get_info_from_database: unit of measure not found

so still unable to use the conversion functionalities.

heres the output of gdalinfo for this issue (with 5.1.0) (color palette is removed for convenience)

Driver: GTiff/GeoTIFF Files: gbr_lfc-day_gsgs_20130919_lcc.tif Size is 18004, 24604 proj_uom_get_info_from_database: unit of measure not found Coordinate System is: PROJCRS["Lambert Conformal Conic; WGS84; WGS84", BASEGEOGCRS["WGS_1984", DATUM["World Geodetic System 1984", ELLIPSOID["WGS 84",6378137,298.257223563, LENGTHUNIT["metre",1]], ID["EPSG",6326]], PRIMEM["Greenwich",0, ANGLEUNIT["unknown",0.0174532925199433]]], CONVERSION["Lambert Conic Conformal (2SP)", METHOD["Lambert Conic Conformal (2SP)", ID["EPSG",9802]], PARAMETER["Latitude of false origin",54.375, ANGLEUNIT["degree",0.0174532925199433], ID["EPSG",8821]], PARAMETER["Longitude of false origin",-3.3, ANGLEUNIT["degree",0.0174532925199433], ID["EPSG",8822]], PARAMETER["Latitude of 1st standard parallel",57.3333333333333, ANGLEUNIT["degree",0.0174532925199433], ID["EPSG",8823]], PARAMETER["Latitude of 2nd standard parallel",49.3333333333333, ANGLEUNIT["degree",0.0174532925199433], ID["EPSG",8824]], PARAMETER["Easting at false origin",0, LENGTHUNIT["metre",1], ID["EPSG",8826]], PARAMETER["Northing at false origin",0, LENGTHUNIT["metre",1], ID["EPSG",8827]]], CS[Cartesian,2], AXIS["easting",east, ORDER[1], LENGTHUNIT["metre",1, ID["EPSG",9001]]], AXIS["northing",north, ORDER[2], LENGTHUNIT["metre",1, ID["EPSG",9001]]]] Data axis to CRS axis mapping: 1,2 Origin = (-354481.960000000020955,661473.700000000069849) Pixel Size = (50.000000000000000,-50.000000000000000) Metadata: AREA_OR_POINT=Area TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch) TIFFTAG_XRESOLUTION=254 TIFFTAG_YRESOLUTION=254 Image Structure Metadata: COMPRESSION=LZW INTERLEAVE=BAND Corner Coordinates: Upper Left ( -354481.960, 661473.700) ( 9d39'44.27"W, 60d10'13.56"N) Lower Left ( -354481.960, -568726.300) ( 8d 9'41.01"W, 49d 8'45.62"N) Upper Right ( 545718.040, 661473.700) ( 6d27'33.75"E, 59d58'40.26"N) Lower Right ( 545718.040, -568726.300) ( 4d10' 5.65"E, 48d59'51.66"N) Center ( 95618.040, 46373.700) ( 1d48'37.91"W, 54d47' 0.74"N)