In the newest Ruins version (1.14.4.1) Templates that contain the rule 'preserveBlock' will not spawn correctly.

Attempting to spawn these templates with the /testruin command results in the chat message "EventRuinTemplateSpawn returned as canceled, not building that."

If the template is generated naturally it will result in large air pockets where the structure should be.

I tested this issue on templates made by well-known creators like Gillymoth & Jordan_Peacock and the issue still shows up. Templates without this rule generate fine

@AtomicStryker
For those wondering how to do so, how does one re-parse the old structures?

Basically spawn them in a compatible version of MC/Ruins, load the savegame in current MC/Ruins, place baseplate of blocks (see template parser tutorial), parse, edit template file to taste.

yes even with downloaded templates this still does not work

I doubt the templates you were trying to use were compatible with 1.13/1.14. The format has changed. You need to re-parse older structures if you want them as templates.