hi! hmm i think this problem is related to a folders migration logic we run when you update to any version > 2.3.0.
are you storing your templates using fs-store?
this is a similar topic https://forum.jsreport.net/topic/1262/error-because-of-folder-shortid/6 in which i ask for some help to reproduce the issue so we can fix it, maybe you can help us sharing your original entities (the entities previous the jsreport upgrade to 2.4.0), you can share a zip of your data folder and your config file privately via email if you want to help us to fix this. unfourtunately this is the best way for us to replicate the problem, since we are not able to replicate the same issue, so it probably means that it is only affecting some specific migrations and your case will help to verify this.
quote from the other topic:
are you able to replicate the issue every time you upgrade the jsreport? i mean, if you go back to your previous jsreport/jsreport:2.0.0-full image with the same data folder that you have at that time, and then try to upgrade to jsreport/jsreport:2.6.1-full, does the issue continues to happen every time? if this is something you can reproduce every time you try to migrate from jsreport/jsreport:2.0.0-full to jsreport/jsreport:2.6.1-full then best will be that you share with us the data folder that you have on jsreport/jsreport:2.0.0-full so we can inspect what is happening, since the addition of folders entities to jsreport (v2.3.0) there is a migration step that we run at jsreport startup that tries to migrate entities to folders, it can be the case that this migration is causing this issue by duplicating the shortid, however we never saw this before.