Reproduction steps:
1. Open attached project "Rect2D_Vs_TextMeshProUGUI.zip"
2. Open "SampleScene" scene in the "Scenes" folder
3. Locate "RMVTMP" prefab in the "prefabs" folder
4. Drag and drop the prefab on "Canvas(Drag RMVTMP Here)" GameObject in the Hierarchy
5. Select the newly created instance of "RMVTMP" and disable the GameObject through the Inspector
6. Enter Play Mode
7. Enable and disable "RMVTMP" GameObject multiple times

Expected result: The text is not visible since the RectMask2D is applied
Actual result: The text appears for a single frame (RectMask2D is ignored for the frame)

Reproducible with: 2.1.6 (2019.4.25f1), 3.0.6 (2020.3.7f1), 3.0.6 (2021.1.5f1), 3.0.6 (2021.2.0a17)
Could not test with: 2018.4 (errors)

Notes:
1. Only reproducible if the scene is not saved after adding the GameObject with TextMeshProUGUI
2. If the GameObejct added is disabled already the issue is not reproducible until the GameObject is enabled and disabled again