Summary
On accounts with a large owned-content library, the Epic Games Launcher cannot install any Fab / Unreal Engine Marketplace content. Every install is blocked because the launcher enumerates owned catalog items in a single QueryItems request that exceeds the catalog service’s hard limit of 1000 IDs per request. The service rejects the entire batch with HTTP 400 (errors.com.epicgames.catalog.invalid_count), the owned-item enumeration never completes, and the launcher can therefore never resolve the catalog item → download manifest needed to start the install.
The launcher is not chunking/paginating the ID list into batches of ≤1000, so any account whose enumeration list exceeds 1000 IDs is permanently unable to install Fab content via the launcher.
What type of bug are you experiencing?
Plugins
URL where the bug was encountered
Steps to Reproduce
Sign into the Epic Games Launcher on an account with a very large Fab/Marketplace library (>1000 owned catalog items).
Navigate to any Fab listing in the launcher, e.g. com.epicgames.launcher://fab/plugins/egl/listings/963d38ea-f002-41a7-8f3e-5ca7e3b0cb79 (web URL: rdTexTools (rd Tools Pro) | Fab).
Click Add to Project / Install.
Observe that the download/install never starts (fails silently).
Expected Result
The launcher batches owned-item catalog lookups into requests of ≤1000 IDs (or however the service requires), the enumeration completes, and the selected Fab content downloads and installs.
Observed Result
The launcher issues a single QueryItems catalog request containing 1,255 IDs. The catalog service rejects the whole request with HTTP 400. The item repository is never populated, so subsequent per-item resolution fails and the install cannot start.
Platform
Epic Games Launcher (Portal) version: 20.1.3-0+UE5
Launcher build/AppVersion: 86741129d105f816e1eeaf52744f7b866890e645
Launcher engine base: 5.5.4-0+UE5
OS: Windows 11 Pro, build 10.0.26200
Installed engine used for verification: Unreal Engine 5.8 (with FabPlugin_5.8)
Owned/entitled apps on account: ~8,386 (LogCommunityPortalOSS: …found 8386 entitled apps)
Failing service host: catalog-public-service-prod06.ol.epicgames.com
Operating System
All (Tested on Linux / Windows)
Additional Notes
Root Cause (from client logs)
The launcher’s owned-content enumeration builds one oversized catalog request:
LogOnline: Warning: OSS: Invalid response.
CorrId=UE5-d5e3070394494a909172f803e6ab15fe-D6CEC785474D82E9632D108A8B6DDFE7-84F7E76B4DBE29A72A2318868FE0509A
code=400
errorcode=errors.com.epicgames.catalog.invalid_count
errormessage=Sorry, the ids count ‘1255’ should not be greater than 1000.
errorraw={“errorCode”:“errors.com.epicgames.catalog.invalid_count”,
“errorMessage”:“Sorry, the ids count ‘1255’ should not be greater than 1000.”,
“messageVars”:[“ids”,“1255”],“numericErrorCode”:5201,
“originatingService”:“com.epicgames.catalog.public”,“intent”:“prod”}
LogOnline: Warning: OSS: QueryItems request failed: Sorry, the ids count ‘1255’ should not be greater than 1000.
Because that enumeration fails, downstream item lookups the installer depends on come back unfulfilled:
LogPortalCatalog: Error: FItemRepository(poodle)::RequestById() - Request for Item unfulfilled
because neither an enumeration has happened or on demand mode been enabled.
No download manifest is ever requested, and no BuildPatchServices download is started for the selected item.
Evidence — representative occurrences (same account, multiple sessions)
Timestamp (log, UTC) CorrId Result
2026.07.09-01.19.35 …-7505D9E242894A75B0C67A8518490092 400 invalid_count, ids=1255
2026.07.09-01.43.30 …-FB1E7FF648C702917E883CA55AB16004 400 invalid_count, ids=1255
2026.07.10-19.31.38 …-84F7E76B4DBE29A72A2318868FE0509A 400 invalid_count, ids=1255
(Shared request prefix on all: CorrId=UE5-d5e3070394494a909172f803e6ab15fe-D6CEC785474D82E9632D108A8B6DDFE7-…)
Total invalid_count failures in the current log: 189, ID count always exactly 1255.
Downstream Request for Item unfulfilled … enumeration errors: 33.
First seen in current log: 2026.07.09-01.19.35; most recent: 2026.07.10-19.31.38.
Suggested Fix
Client-side: split the owned-item catalog enumeration into batches of ≤1000 IDs (paginate QueryItems) and merge results, or enable the “on demand” item-resolution mode referenced in FItemRepository. Server-side alternative: raise/relax the 1000-ID cap for authenticated owned-content enumeration. The client should also not treat a single over-limit batch as a hard failure of the entire enumeration.