It looks like the Tories in the House of Lords had a different (and arguably important) reason for the filibuster, and it wasn't something decided by Boris or Tory MPs. It wasn't the case that they didn't want the new law to pass, but rather, they were opposed to the guillotine motion Baroness Smith of Basildon (Labour) wanted to introduce to make sure the bill was passed on time. The Tory peers believed the guillotine motion would introduce a dangerous precedent for the future: they argued that the key feature of the House of Lords is that they take as much time as it is needed to discuss and amend the bills. To quote Earl Howe (Conservative):
I will make some brief remarks on the amendment of my noble friend. I focus, as other noble Lords will do, on the practical effects of this Motion. Its main effect, as has been said, is a guillotine. Setting aside the issue of precedent, I do not think that one can dismiss this as some kind of run-of-the-mill measure. The practical effects of the guillotine will be wide ranging and deeply damaging to the ability of the House to scrutinise legislation as fully as it needs to.
In the end, Labour and Tory peers came to agreement: Labour wouldn't introduce the guillotine motion, and the Tories wouldn't obstruct the proceedings and would make sure that the bill completes the passage through the Lords by 5pm on Friday. To quote Lord True (Conservative):
It is extraordinary that, when one is trying to round something off amicably, some people mutter in that way. The purpose of all the amendments—the noble Baroness on the Front Bench opposite was extraordinarily gracious on this point—was to guard against the guillotine, something that the noble Baroness said was not desirable in this House. As far as I am concerned, we will give an undertaking that we will abide by any usual channels agreement, as Back-Benchers in this House always do. Certainly, if another attempt is ever made to bring forward a guillotine Motion of this kind, it can expect the same sort of resistance, irrespective of the issue concerned.
The details are in the House of Lords Hansards from 4 September 2019. The agreement was announced at 1.09 am.