The majority of those seem to be TrEMBL, unreviewed (computer annotated) entries from UniProtKB and could explain the absence of results from Reactome. O70209, Q91YJ3, Q91YJ5, Q8BM55 seem to be reviewed though. See more about those statuses here. It seems Reactome is human centric, so perhaps the above SW entries from mouse are still to be inferred from the human pathway counterparts? Human TrEMBL does not return any results in BioMart .e.g Q9NQR3 and Q15505. It may be a good idea to contact Reactome for a definitive answer.

Mapping non-Reactome ids to Reactome Events (Pathways or Reactions) when not considering any statistics:

library(ReactomeContentService4R)
#> Connecting...welcome to Reactome v77!

uniprot.id <- 'O95602'
pathways <- map2Events(uniprot.id, resource = "UniProt", species="human", mapTo = "pathways")

dim(pathways)
#> [1]  5 14
head(pathways, 1)
#>     dbId                               displayName         stId    stIdVersion
#> 1 427413 NoRC negatively regulates rRNA expression R-HSA-427413 R-HSA-427413.2
#>   isInDisease isInferred
#> 1       FALSE      FALSE
#>                                                                                                              name
#> 1 NoRC negatively regulates rRNA expression, Methylation of histones and DNA negatively regulates rRNA expression
#>   releaseDate  speciesName                    doi hasDiagram hasEHLD
#> 1  2014-03-12 Homo sapiens 10.3180/REACT_200856.1       TRUE   FALSE
#>   schemaClass className
#> 1     Pathway   Pathway

^{Created on 2021-07-23 by the [reprex package](https://reprex.tidyverse.org) (v2.0.0)}