Please report suspected bugs to Oracle using your MOS account.
Has anyone ever seen this?
Not with 17.4. For the 4.2, however, you can find several discussions on this matter. For example...
On Windows 10, jdk1.8.0_151, the connection reset does not reproduce using either...
1. The JDBC Thin driver shipped with 17.4
2. The JDBC OCI/Thick driver in Oracle Instant Client 12.2. (Configurable in Database > Advanced preferences)
Is your environment different? Perhaps you use a different JDBC driver from an older Oracle client?
I'm using Windows 10, the jdk that is included in SQL Developer download and I have an 11g client installed.
I managed to get a fresh 12c client installed instead. Then I re-downloaded SQL Developer 17.4, deleted any roaming leftover, extracted it to C:\sqldeveloper and ran it. Then I setup it to finally use the thick driver:
Then I connected to my PDB (yeah, the problem only happens with that) instance but I got the same odd issue:
I started to think that I've been cursed to stick with 4.1 LoL
have you checked your database's Alert Log?