Number 3 happens all the time to me when using VSCode with Copilot as autocomplete. Copilot sometimes works, sometimes doesn't. Also happens a lot when using Pycharm with Python. Sometimes it's great at autocompleting, sometimes it completely gets lost and has no idea what my Python script is doing.

Number 5 also happens a lot on VSCode + Platformio. It also frequently happens on Intellij IDEA for me, but mostly when I am concurrently running build or test while writing. My crappy work laptop suffers from Windows 11 related performance issues, and when there's not enough performance available, underlines do get wonky quite frequently.