SolrException: Unknown encoder: html (DSpace 8.3)

[Urban Andersson]

Hello all,

I'm doing a local test upgrade from 8.1 to 8.3 on MacOS (Solr version 8.11.4) and I have run into an issue that I just cannot get my head around.

Searching is not working properly, resulting in some lists not rendering etc. 
Browse functions work. Search index is created correctly and I can also access it, and it looks ok and is fully searchable from Solr admin, without issues.

dspace log:

2026-02-13 09:05:33,056 ERROR 2654b549-738c-46dd-8fb3-24a02ba05b5e 189ac324-0aad-437f-ba3f-746d2b764ad9 org.dspace.app.rest.repository.DiscoveryRestRepository @ Error while searching with Discovery
org.dspace.discovery.SearchServiceException: Error from server at http://localhost:8983/solr/search: Unknown encoder: html
at org.dspace.discovery.SolrServiceImpl.search(SolrServiceImpl.java:784)
at org.dspace.discovery.SolrServiceImpl.search(SolrServiceImpl.java:763)
at org.dspace.app.rest.repository.DiscoveryRestRepository.getSearchObjects(DiscoveryRestRepository.java:107)
at org.dspace.app.rest.DiscoveryRestController.getSearchObjects(DiscoveryRestController.java:156)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:578)

solr.log:

2026-02-13 09:05:33.018 INFO  (qtp1341706533-85) [   x:search] o.a.s.c.S.Request [search]  webapp=/solr path=/select params={q=*:*&fl=dateIssued.year,search.resourcetype,search.resourceid,search.uniqueid,database_status&start=0&fq=(search.resourcetype:Item+AND+latestVersion:true)+OR+search.resourcetype:Collection+OR+search.resourcetype:Community&fq=-withdrawn:true+AND+-discoverable:false&fq=location:l67384c88-38f3-4f99-b727-e16535ef2def&fq=location:l67384c88-38f3-4f99-b727-e16535ef2def&fq=&fq=dateIssued.year:[*+TO+*]&sort=dateIssued.year_sort+desc&rows=1&wt=javabin&version=2} hits=1 status=0 QTime=1
2026-02-13 09:05:33.021 INFO  (qtp1341706533-87) [   ] o.a.s.s.HttpSolrCall HttpSolrCall.init(http://localhost:8983/solr/search/select?null)

2026-02-13 09:05:33.053 ERROR (qtp1341706533-87) [   x:search] o.a.s.h.RequestHandlerBase org.apache.solr.common.SolrException: Unknown encoder: html => org.apache.solr.common.SolrException: Unknown encoder: html
at org.apache.solr.highlight.DefaultSolrHighlighter.getEncoder(DefaultSolrHighlighter.java:360)
org.apache.solr.common.SolrException: Unknown encoder: html
at org.apache.solr.highlight.DefaultSolrHighlighter.getEncoder(DefaultSolrHighlighter.java:360) ~[?:?]


There is no HtmlEncoder in the Solr configs, but I don't think there should be either, and I guess this is something else going wrong? 

If someone could give me a hint on what I should be looking for it would be really appreciated.

Many thanks!