Calibre when opening some books viewer is hung at 'Loading next section'

[tomdean]

> uname -a
Linux meerkat 5.8.0-59-generic #66~20.04.1-Ubuntu SMP Thu Jun 17 11:14:10 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
> lsb_release -rd
Description: Ubuntu 20.04.2 LTS
Release: 20.04
> apt-cache policy calibre
calibre:
  Installed: 4.99.4+dfsg+really4.12.0-1ubuntu1
  Candidate: 4.99.4+dfsg+really4.12.0-1ubuntu1
  Version table:
 *** 4.99.4+dfsg+really4.12.0-1ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu focal-updates/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu focal-updates/universe i386 Packages
        100 /var/lib/dpkg/status
     4.99.4+dfsg+really4.12.0-1build1 500
        500 http://us.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu focal/universe i386 Packages

Recently, when opening some books the viewer hangs with the message
   'Loading next section...Please wait'
I waited 10 minutes and the viewer was still hung.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: calibre 4.99.4+dfsg+really4.12.0-1ubuntu1
ProcVersionSignature: Ubuntu 5.8.0-59.66~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-59-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: GNOME
Date: Mon Jul 5 00:15:10 2021
InstallationDate: Installed on 2021-05-22 (44 days ago)
InstallationMedia: Ubuntu 20.04.2.0 LTS "Focal Fossa" - Release amd64 (20210209.1)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: calibre
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.