Sort is not sorting?

I seem to be having the same issue as described in https://unix.stackexchange.com/questions/562256/the-join-utility-reports-file-is-not-sorted-but-in-fact-it-is-sorted however I have piped BOTH files through sort before attempting to join. I have also tried sort -d and sort -g. This is running on Amazon Linux 2, using sort from coreutils-8.22-24 The following illustrates the issue:

root@host:/home/user# cat /tmp/db_schema_size | sort
directory       0.000106811523
directory_1      1.059814453265
directory_123    0.564987182688
directory_123123 0.564987182688
directory_1234   0.564987182688
directory_12345  0.564987182688
directory_1234567        0.564987182688
directory_82473  0.934677124123
directory_82475  0.751586914161
directory_82477  0.881881713968
directory_82479  0.751571655373
directory_82481  0.750396728614
directory_82483  0.589370727610

root@host:/home/user# cat /tmp/db_dir_sizes | sort
directory       132
directory_1      1115936
directory_123123 613244
directory_12345  613248
directory_1234567        613248
directory_1234   613244
directory_123    613244
directory_82473  1015140
directory_82475  818764
directory_82477  958628
directory_82479  818756
directory_82481  817500
directory_82483  638820

Both files are the same structure - no lead/trailing whitespace, a single tab char between the values. Both files are processed by sort but produce output in a different order. I do see that on Ubuntu 22.04 LTS, the output is consistent (and of the first form above). What am I missing here? **update** For clarification... On AWS Linux 2 with LANG=en_US.UTF-8, I get output as above - i.e. output differs On AWS Linux 2 with LANG=C.UTF-8 output is the same On Ubuntu with both LANG=C.UTF-8 and LANG=en_US.UTF-8, output is the same