We're experiencing a severe error with JCE as the frontend editor:
Browsing through the Joomla Site, the Web Server says "502 - Bad Gateway" every now and then.
In the only category set to working with JCE by default, no article can be displayed in full.
Because in all other categories (which are built without frontend editing and therefore without JCE) this phenomenon doesn't show.

This is our setup:

Joomla 3.9.3
JCE Pro 2.7.13 (this phenomenon started with version 2.7.11 already)
Helix 3 template version 2.5.6

@support: the backend access is open for you to check.

This one for example, and several other in this Joomla category, which is the only one you can frontend-edit an article as a registered user:

https://www.plcnext-community.net/index.php?option=com_content&view=article&id=380:modbus-tcp-with-python-on-axc-f-2152&catid=78&lang=en&Itemid=366

It occurs when somebody tries to show the whole article, by clicking the "read more..." link or the articles' title.

Happens randomly, but in all browsers, from within and outside the company's network, and being logged in with different user types, even just viewing as "Guest" user.
We already tried to clear caches in both Joomla and browsers. Sometimes it seems like everything is okay when first approaching the website in a cleared browser or logged out, but it always comes back and bites us in the a...

Thank for checking, Ryan!