AssertionError: Module ZODB.blob, line 435, in getPathForOID

Anyone seen this error when POST to plone.restapi (Plone 5.2.1, Python 3)?

This happened during a migration phase with images. Possibly related to a low-memory situation (although only 14,2 GB out of 15,7 GB used, no swapping issue, enough FS resources)

2020-05-12 09:37:45,454 ERROR   [Zope.SiteErrorLog:251][waitress] 1589269065.4233440.9204063557356513 http://localhost:20081/plone_portal/img/dbz/diversiteit-en-gender/ugentinzicht/POST_application_json_
Traceback (innermost last):
  Module ZPublisher.WSGIPublisher, line 162, in transaction_pubevents
  Module transaction._manager, line 252, in commit
  Module transaction._manager, line 131, in commit
  Module transaction._transaction, line 311, in commit
  Module transaction._compat, line 50, in reraise
  Module transaction._transaction, line 302, in commit
  Module transaction._transaction, line 447, in _commitResources
  Module transaction._compat, line 50, in reraise
  Module transaction._transaction, line 421, in _commitResources
  Module ZODB.Connection, line 497, in commit
  Module ZODB.Connection, line 546, in _commit
  Module ZODB.Connection, line 595, in _store_objects
  Module ZODB.mvccadapter, line 170, in storeBlob
  Module ZEO.ClientStorage, line 586, in storeBlob
  Module ZODB.blob, line 435, in getPathForOID
AssertionError

The assert shows that creating the path for storing a blob failed.
Given that it is a ZEO ClientStorage, might it be that the tmp mount was full?
Assuming you have your client cache on a tmp mount, that is.

We don't have the OSError, so I'm guessing here.