I don’t get the first 2 videos either but the third one after the 23-second mark, shows the same, or a very similar, bug I commented here. My reply includes GIFs that may help understand the issue and, maybe, both topics are related, otherwise my reply should be moved here.
Edit: if someone is having this or similar problems should try disabling Gboard settings that start with “Auto” in Settings > Preferences and the ones related to suggestions in Settings > Corrections & Suggestions. I think that or maybe a Gboard update is what solved this for me.