Evolution renders email attachments for a long time

[Nicholas Guriev]

1. Import an attached mbox file containing an email from debian-devel list which consists of ten nested messages.
2. Open that digest email.
3. It will take 35 seconds before UI becomes interactive again. An area with the email is blocked for all the time.
4. I'd expect the whole email to render in less then a second.

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: evolution 3.38.2-1
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu55
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.456
CurrentDesktop: ubuntu:GNOME
Date: Fri Dec 18 06:09:14 2020
LiveMediaBuild: Ubuntu 21.04 "Hirsute Hippo" - Alpha amd64 (20201216)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: evolution
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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

[Bruce Pieterse (octoquad)]

I'm seeing a similar problem occurring in Ubuntu 18.04 with Evolution 3.28.5-0ubuntu0.18.04.2 with a new e-mail being composed and attaching or detaching a local file with a size of 65KB which hangs Evolution for about 20-30 seconds.

This problem did not occur on a previous versions of Evolution. Additionally this is running on LTSP Fat Clients via SSH home mounts.

I'm not sure if my issue and this issue is related. Let me know if I need to submit a new bug report instead. Happy to provide any debugging information as well.