Text annotation exported to pdf not readable on iPad

Bug appeared about 10 days ago.
The text characters show as empty boxes on an iPad (uptodate, iPad air 2), opening pdf from mail attachment.

I can detect the following differences in exported PDFs before and after bug:
pdffonts: toUnicodemap was 'yes' before, now 'no'
pdfinfo: the lines

Producer: cairo 1.15.10 (http://cairographics.org)
CreationDate: Wed Nov 18 15:12:28 2020 CET

are now missing.

Export with 'legacy pdf export' has no effect.

      Best ... Peter Glassel

I am on Ubuntu 18.04.5 LTS

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: xournal 1:0.4.8-1build1
ProcVersionSignature: Ubuntu 4.15.0-126.129-generic 4.15.18
Uname: Linux 4.15.0-126-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.20
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Dec 11 11:56:41 2020
InstallationDate: Installed on 2020-04-24 (230 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: xournal
UpgradeStatus: No upgrade log present (probably fresh install)