Memory issues after update to SS4.3

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Silverstripe Version: SS 4.4.3

We recently updated a website from 4.1.2 to 4.4.3. After the update suddenly we got a lot of memory issues, not on the frontend-part but only on the backend. And not for all members, but only for administrators.

These memory error appears on several parts of the CMS, but mostly on the ModelAdmins (not the edit-screens). Like on admin/pages, admin/settings or admin/subsites.

Although there is a lot of data in the database, the parts where it’s complaining about the memory is always on relatively small datasets. For example there are only 15 records in subsites, and 5 pages per subsite.

The error is always the same:

[Alert] Allowed memory size of 536870912 bytes exhausted (tried to allocate 1048576 bytes)

Line 143 in /var/www/vhosts/client.com/httpdocs/vendor/silverstripe/framework/src/ORM/Connect/PDOStatementHandle.php

The only other thing that might have to do with this, is we als updated from PHP 7.1 to PHP 7.2 around the same date. We already bumped the memory-limit to 512, but that seems to be insufficient.

It is not giving errors every time, but rather random (or maybe only after flush)

Does anyone has a clue what is causing this? Is it database related (since it is always on PDOStatementHandle.php)?