V5.0 math equations difficult to read in V5.1

I received on the PCLinuxOS forum a document with Math equations that appear normally
in Writer version 5.0.
The same document is read with difficulty in version 5.1 using temporarily
about 3GB memory for a 15KB document.
The equations do not appear in the screen
Once the equations have been opened and closed again,
they are seen on the screen, and after that the document opens normally
in V5.1.

My questions:

  1. What has changed between versions 5.0 and 5.1 with respect to equations?
  2. Has there been a format change?
  3. If so, is there an easy way to update a bunch of documents with a lot of equations?


Build ID: d3bf12ecb743fc0d20e0be0c58ca359301eb705f
CPU Threads: 2; OS Version: Linux 4.4; UI Render: default;
Locale: en-US (en_US.UTF-8)
Linux Kernel: 4.4.4-pclos1 x86_64 (64 bit) Desktop: MATE 1.14.0 Distro: PCLinuxOS