The page shows naked tag code instead of html

Good afternoon. The main page of our site began to display incorrectly. The columns are no longer displayed. Everything was fine for a few years and today it broke.

The page shows naked tag code instead of html. For example:

<em>[tdc_zone zone_shadow_shadow_offset_vertical="0" h_display=""][vc_row row_divider_bottom=""][vc_column width="1/3" tdc_css="eyJhbGwiOnsib3BhY2l0eSI6IjkwJSIsImRpc3BsYXkiOiIifX0="]</em>

We have a Newspace theme and tagDiv Composer Version 2.3. This is an old version (only it works stably with our plugins).

When we enter the wp-admin (administrative panel of the site) and then to the Pages section, we see that the page title no longer displays the ability to change the page using blocks (tagDiv Composer). This button is gone.

What happened? And what should we do?

Addition.

It looks like the plugins (tagDiv Composer, tagDiv Newsletter, tagDiv Social Counter) have been deactivated by something.

We activated the tagDiv Composer plugin – and the site page began to display normally. It is not yet clear if there are other problems.

And the first question. How could the plugin deactivate itself?

We use old version (Version 9.5). This is the most stable version and is the only one that works well with some of our old plugins. There were no problems for many years. Now there is a problem as described above.

We cant update plugin and theme. But ealier we hadnt problem with this plugin. It`s true that plugin are deactivated.

But I see.

We can not update plugin and theme. But ealier we had not problem with this plugin. It`s true that plugin are deactivated.

But I see.