Since the engine didn't heat up, I'm more suspicious of the oil pump than the strainer. Both pumps pull from the same strainer. If it were blocked, I think the engine would have heated up because the front pump runs oil up through the cylinders for cooling and then out to the oil cooler.
If it turns out that the problem was caused by something that was probably a manufacturing defect, it would be a good idea to contact Triumph. Never know if they might give you some help with the repairs as a goodwill thing.
