Based on the information provided, it seems like there might be an issue with how Tabby is handling completions in IntelliJ. The event log you've shared indicates that the completions are being triggered, but they are not providing the expected multiline output. This could be due to a number of reasons, such as a configuration issue, a bug in the Tabby IntelliJ plugin, or an incompatibility with the specific version of IntelliJ you're using. To troubleshoot this further, you could try the following steps:

1. Ensure that the Tabby plugin is up to date in IntelliJ.
2. Check if there are any known issues with the Tabby plugin for your version of IntelliJ.
3. Try resetting the Tabby plugin settings to default.
4. If possible, test with a different version of IntelliJ to see if the issue persists.
5. Reach out to Tabby support with the event log and screenshot for more detailed assistance.