Brand and model of the missing devices? Also, were you using custom DTHs for them?
Unfortunately this has happened to some people during the migration:
New SmartThings App: Half my devices are missing but IDE shows them
Brand and model of the missing devices? Also, were you using custom DTHs for them?
Unfortunately this has happened to some people during the migration:
New SmartThings App: Half my devices are missing but IDE shows them