Espressione di EF core valutata localmente ... perché?

Ho un metodo fuori dal mio contesto db che assomiglia a questo:

    public override async Task<IEnumerable<FeedMessage>> GetLatestFeeds(
        int userId,
        int groupId,
        int maxResults = 15,
        long lastId = 0)
    {
        if (lastId == 0) lastId = long.MaxValue;

        var userSpecific = 
            FeedMessages.Where(fm =>
                fm.UserId.HasValue && fm.UserId.Value == userId && fm.Id < lastId && !fm.IsDeleted);

        var groupSpecific = 
            FeedMessages.Where(fm =>
                fm.UserId == null && fm.GroupId.HasValue && fm.GroupId.Value == groupId && fm.Id < lastId && !fm.IsDeleted);

        var siteWide = 
            FeedMessages.Where(fm =>
                fm.UserId == null && fm.GroupId == null && fm.Id < lastId && !fm.IsDeleted);

        var feeds = await
            userSpecific.Union(groupSpecific).Union(siteWide)
                .OrderByDescending(x => x.Id)
                .Take(maxResults)
                .ToListAsync();

        return feeds.OrderBy(x => x.Id);
    }

l'idea qui è che voglio prendere i record che sono specifici per utente, specifici per gruppo o generici, organizzarli per ID e restituire i primi risultati X.

Se eseguo questo ottengo un'intera schermata di errori:

warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where ((((([fm].UserId == null) AndAlso ([fm].GroupId != null)) AndAlso (Convert([fm].GroupId, Int32) == __groupId_2)) AndAlso ([fm].Id < __lastId_3)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where (((([fm].UserId == null) AndAlso ([fm].GroupId == null)) AndAlso ([fm].Id < __lastId_4)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where ((((([fm].UserId == null) AndAlso ([fm].GroupId != null)) AndAlso (Convert([fm].GroupId, Int32) == __groupId_2)) AndAlso ([fm].Id < __lastId_3)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where (((([fm].UserId == null) AndAlso ([fm].GroupId == null)) AndAlso ([fm].Id < __lastId_4)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'orderby [x].Id desc' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Take(__p_5)' could not be translated and will be evaluated locally.

Che cosa sta succedendo qui? E come lo aggiusto? Questo sarà un grande tavolo, la valutazione locale schiaccerà il sistema.