I am using this code to extract the lengths of genes directly from ensemble:

  ensembl = useEnsembl(biomart="ensembl", dataset="hsapiens_gene_ensembl")
  genelength =  getBM(attributes=c('ensembl_gene_id','ensembl_transcript_id', 'transcript_length','cds_length'), filters =  'ensembl_gene_id', values = rownames(counts), mart = ensembl, useCache = FALSE)
  gene_canonical_transcript =  getBM(attributes=c('ensembl_gene_id','ensembl_transcript_id','transcript_is_canonical'), filters =  'ensembl_gene_id', values = rownames(counts), mart = ensembl, useCache = FALSE)
  gene_canonical_transcript_subset = gene_canonical_transcript[!is.na(gene_canonical_transcript$transcript_is_canonical),]
  genelength = merge(gene_canonical_transcript_subset, genelength, by = c("ensembl_gene_id", "ensembl_transcript_id"))
  return(genelength)

This however doesn't always work, I really don't know why it works only 50% of the time. Sometimes it uses mirror sites:

Ensembl site unresponsive, trying uswest mirror

sometimes it works perfectly fine without using mirror sites, and sometimes it fails completely, producing this error:

Error in bmRequest(request = request, httr_config = httr_config, verbose = verbose) :
Gateway Timeout (HTTP 504).

What causes this to be so unstable? I mean, the code works just fine (it gives gene lengths when it runs without any errors). Is the problem with the package? or with the site itself? is there anyway to avoid this error?

Thank you.