Hi @Aclassifier,
We are integrating the newly release 19.5.4 firmware release in the following pull requests:
- Bump latest model B version to19.5.4 by sandeepmistry · Pull Request #195 · arduino-libraries/WiFi101 · GitHub
- Add new WINC1500 19.5.4 firmware by sandeepmistry · Pull Request #11 · arduino/WiFi101-FirmwareUpdater-Plugin · GitHub
I don't think the 19.5.3 release was ever integrated into Atmel Studio, so we had no access to those binaries.