[Page Title] suddenly not showing up after months of working fine

[JAPAN_IMO]

Hi there, I've had my all my Pages' title and Meta description running fine since the publishing of my site and everything worked fine.

However, recently I started to notice the title of every single page on the site, including the homepage, is not showing up properly. It displays the link of the web site ONLY, instead of the actual title that I've set and was running fine for many months.

I recently deleted a SEO plug-in, and I wonder if that has impacted anything? However, I'm not sure when this started happening as I didn't notice until now.

I have not changed any other settings on each page / homepage, so all the Search engine listing titles are still the same/untouched.

Please provide any insights that can help! Thank you.