I'm trying to create an index for GRCh37. I get the error below despite having loads of memory.

I'm running Ubuntu 20.10 in WLS2.

(base) balter@winmac:~$ bwa index -a bwtsw Homo_sapiens.GRCh37.dna.toplevel.fa
[bwa_index] Pack FASTA... 396.80 sec
[gzclose] buffer error
(base) balter@winmac:~$ free -mh
              total        used        free      shared  buff/cache   available
Mem:           50Gi       126Mi        33Gi       0.0Ki        16Gi        49Gi
Swap:          13Gi          0B        13Gi
(base) balter@winmac:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.10
Release:        20.10
Codename:       groovy