Reproduction steps:
1. Open the attached “IN-126647” project
2. Open the “Scenes/SampleScene” Scene
3. Select the “Canvas/Text (TMP)” GameObject in the Hierarchy window
4. Set text to “<a>text</a>” under the “TextMeshPro - Text (UI)” Component in the Inspector window
5. Observe the Console

Actual result: “IndexOutOfRangeException: Index was outside the bounds of the array.” or “NullReferenceException: Object reference not set to an instance of an object” error is thrown
Expected result: No errors are thrown

Reproducible with: 2023.1.0a20 (be935afddb32), 6000.0.64f1, 6000.3.2f1, 6000.4.0b2, 6000.5.0a3
Not reproducible with: 2023.1.0a19 (0c2ff406cf78)

Reproducible on: Windows 11, Ubuntu 25.04
Not reproducible on: No other environments tested

Workaround: “IndexOutOfRangeException” error can be fixed by adding a “href” value to “<a>” tag

Note:
- Exception thrown depends on which Editor version you’re testing