JDK 11.0.9 jshell's Tab key completion did not work on AIX's dtterm.
(I tested it with AdoptOpenJDK AIX build and my local build)
I tried following steps:
1. Start jshell
2. Type "Sys", then press Tab key
   Tab character is inputted instead of changing to "System"

I could not recreate this issue on JDK 11.0.8.
It may be regression issue for "JDK-8229815 Upgrade Jline to 3.12.1" [1].

Also it worked fine on JDK 15, 16EA.
I could recreate this issue on JDK 14.
It may be regression issue for "JDK-8241598 Upgrade JLine to 3.14.0" [2]

I tried to apply "JDK-8241598"'s changeset "e811fa676a84" [3] against 11.0.9.
This issue was fixed.
Please evaluate upgrading JDK11 JLine to 3.14.0.

[1] https://bugs.openjdk.java.net/browse/JDK-8229815
[2] https://bugs.openjdk.java.net/browse/JDK-8241598
[3] https://hg.openjdk.java.net/jdk/jdk/rev/e811fa676a84