Build 2.8.3_05 introduces a new setting:
"Use Queries for Viewing all Class Instances" in Options > General.
When enabled, opening tree/table views from the schema tab uses queries, which don't have that problem. The default (in previous version and when this setting is unchecked) is a different method, which is usually expected to be more efficient (loading data more lazily), but apparently it is less efficient with slow client-server connections, due to more round trips.
ObjectDB - Fast Object Database for Java (JPA/JDO)