Steps to reproduce:

1. Open Data collection > Discovery > Edit
2. Click to add/edit Checks
3. Choose SNMP V1 and set OID
4. Switch to SNMP V2

Result:
OID value is changes to empty string.

Expected:
When changing Check type values should be remembered. Port value should be changed to default by type only if port value is cleared or it matches previously selected type default value.

This behaviour is present at least since version 5.0.