Hi @sns ,
Does this issue happen to all users? Does this issue still happen if you use some other query ?
1.Please check search setting allow this site or document to appear in search results.
Site level: Settings > Site information > View all site settings > Search and offline availability > Allow this site to appear in search results
Library level: Settings > library settings > Advanced settings > Allow items from this document library to appear in search results
2.Please check whether this search results web part has Hit-highlighted managed properties disappear in search schema.
For Reference: SharePoint unfamiliar error on kw search: SubstrateSearchException: Remote executors failed
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.