Update
I was able to confirm that the download versions of the database can be problematic. This has to do with how the precomputed indexes are hosted by the source. → Usage issues with downloaded snpeff 5.N databases ORG and EU · Issue #6956 · galaxyproject/tools-iuc · GitHub
From here, you can create your own index with the genbank file for you species from NCBI. → FAQ: NCBI reference data
Or, from the fasta and gtf or gff3 files from any other source.
If you need help locating the files you need, we can help. We’ll need to know what indexes you are already using and which server you are working at. The assembly version is important. You could also build your SnpEff index first, get all the reference data prepared, then run the mapping and variant calling against those files instead, to make sure everything is internally consistent.
Hope this helps!