This may be an experiment YouTube is doing, to see whether or not people engage with the site more if the thumbnails are larger. There sometimes are workarounds for this, though unfortunately YouTube doesn't have any easy opt-out feature. You can try some of these however:
Clear cookies. Often, these experiments are cookie-based (with the VISITOR_INFO1_LIVE ...
- youtube-subscriptions-importer on GitHub
This program can be used online to transfer subscriptions. The GitHub page has step-by-step instructions, as well as a link to video instructions.
As mentioned in the official YouTube Help site
Turn off emails from YouTube
To turn off an email notification, click the unsubscribe link at the
bottom of the email. You can also choose to unsubscribe from certain
types of email or all emails from YouTube. Unsubscribe from certain
types of emails
To unsubscribe from certain types of ...
Unfortunately, due to some young abuser who abused the translation system, YouTube has changed the rules. Under the new rules, contributed translations won’t be published to YouTube until the channel owner has manually approved them.
Hopefully, YouTube can figure out a smarter automatic publish mechanism later.
Answering OP question about keyboard shortcut:
The location of close (x) icon (as of 2019 Oct) is one tab back from timeline. As I noted depending on some factors starting active control could be different, so in general solution is as suggested briefly by other answer, I add more details.
If you just skipped (e.g. forward) via timeline, it's active ...
The only way (2019) seems to copy the youtube video raw-url ,i.e. https://www.youtube.com/watch?v=qwFWhqKx42f
1) try that into google or bing search
2) if that doesnt help, search with only id (i.e. qwFWhqKx42f)