Is this a bug? Does not make sense.

See the waterfall the row with red background: https://www.webpagetest.org/result/200526_HP_a06678942bbf131c93968bcd5ee5c2b8/3/details/#waterfall_view_step1

to elaborate on the above, very often now we are getting this resource loading:

2: https://offlinepages-pa.googleapis.com/v1:GeneratePageBundle

from a google search it appears this is a browser invoked check when 3G cuts out or has cut out and internet is restored.

Ofcourse this is sending alarm bells to our SEO partner (SEOWorkers) as it drastically increases page loading time, but this is not something coming from the website at all.

In fact sometimes it appears the page is not fetched at all as if the mobile device has totally lost connectivity.

Fixing this error is outside your control.

If this is important to fix, you’ll open a support ticket with Google… then prepare yourself for no response + maybe someday they’ll fix the problem.