.NET MongoDB Driver - Unsupported Filter Contains

public async Task<Unit> Handle(Query request, CancellationToken cancellationToken)
{
    // Save current questions
    var currentQuestions = (await mongoDatabaseInstance.FindAllAsync<Question>("questions", cancellationToken)).ToList();
    var modified = false;

    try
    {
        if (currentQuestions.Any())
        {
            // We create a filter to only delete questions that are going to be replaced, based on 'Practice'
            // e.g. if we are uploading a spreadsheet that only contains a JAVA sheet, delete all questions where Practice is JAVA
            Expression<Func<Question, bool>> filter = x => request.Questions.Select(x => x.Practice).Contains(x.Practice);

            // Delete all questions and attempt to import new ones
            await mongoDatabaseInstance.DeleteMany("questions", filter, cancellationToken);
        }

        modified = true;
        await mongoDatabaseInstance.InsertMany("questions", request.Questions, cancellationToken);
        return Unit.Value;
    }
    catch (Exception ex)
    {
        // Restore previous questions if there were any and new questions got rejected
        if (currentQuestions.Any() && modified)
        {
            await mongoDatabaseInstance.InsertMany("questions", currentQuestions, cancellationToken);
        }

        throw new Exception($"Error trying to insert questions, file probably doesn't comply with the format.", ex);
    }
}

await MongoDatabase.GetCollection<TDocument>(collectionName).DeleteManyAsync(filter, cancellationToken)

public virtual Task<DeleteResult> DeleteManyAsync(FilterDefinition<TDocument> filter, CancellationToken cancellationToken = default(CancellationToken))
{
    return DeleteManyAsync(filter, null, cancellationToken);
}