Thank you for replying here; this helped me figure out why MAPK10 was missing from my results. It was also marked as a pseudogene in the Ensembl v99 release. It's unfortunate that the Cytoscape app can't use old versions.
I know it's out of your hands for this version, but this may be useful information for future users who find this thread. Querying these missing proteins by gene symbol in Cytoscape currently returns a different protein without notifying the user. Querying VEGFA returns COL18A1 and querying MAPK10 returns DUSP16. The website at least flags these matches for user review but Cytoscape does not. (As always it's just more reliable to use Ensembl or Uniprot ID.)