When using command like

/tellraw @s {"text":"abc","strikethrough":true,"underlined":true}

Observe that the rendered text is problematic.

The strikethrough formatting is not rendered for the last entry of the chat hud and the underline formatting is not rendered for the second last entry of the chat hud (except when subtitles are visible, then they are rendered).

This rendering problems happens as well if the custom text only has strikethrough or only has underlined as well; it is not caused by having two together. e.g.

/tellraw @s {"text":"abc","strikethrough":false,"underlined":true}
/tellraw @s {"text":"abc","strikethrough":true,"underlined":false}

Did not take a screenshot with f3 because there is another bug MC-179839 where characters lose bits when f3 screen is on, so a screenshot without f3 demonstrates the bug best