uniprot sequences occasionally do not get species name when resolving ensembl crossrefs

In 2.11.1
- retrieve the uniprot sequences found by the following query (gene:BACE2 OR gene:BACE1) AND reviewed:yes
These are
  BACE1_HUMAN
  BACE1_MOUSE
  BACE1_RAT
  BACE1_CAVPO
  BACE1_BOVIN
  BACE2_HUMAN
  BACE2_MOUSE
  BACE2_RAT
 -- however, trying these on there own seem to not result in the bug happening...
- retrieve crossrefs to Ensembl (this takes a while)
Mouse over the CDS sequences - most will have a Species:Chromosome dbref, but one mouse or human sequence (so far in my testing) seem to only get the chromosome number, not the species.

I don't see this problem with a smaller number of sequences, suggesting there may be a race condition somewhere in the ensembl fetcher in the vicinity of the Locus construction code.