I haven't crossed the border last week so I can't answer that part of the question directly but I can provide some details on what to expect.
Importantly, it's not like France ever completely gave up random checks or actually reintroduced full-scale systematic border checks. They have mostly been scaled up and down, locally going far beyond what a strict interpretation of the Schengen Borders code would seem to allow, even without formal notification of any kind.
In practice, trains tend to be watched a little more closely than road crossings but it's a long time I haven't seen any visible form of enforcement at the Luxembourg border. Last time I saw some halfway systematic check (everybody had to show ID, no visa/status check) was in Geneva in December 2015. I have not seen any police presence at all when I crossed that border (multiple times) in 2016 and 2017 (and back then the temporary reintroduction notification was definitely in place!)
When checks were in place, they generally take the form of customs or police officers getting on the train at the last station in a foreign country and performing verifications while the train is on the move (seen most recently on the Thalys between Paris and Brussels). You should not expect airport-style checks (à la Eurostar) or being forced to step out.
One exception to this are the train stations in Geneva and Basel, which both have a special platform for trains from France ending there. In that case, everybody gets out of the train and through a border facility not unlike an airport passport check. This can generate queues and delays. As far as I know, these are not generally in use but they haven't been dismantled since Switzerland joined the Schengen area. Through trains calling at Geneva or Basel en route to somewhere else in Switzerland stop in the Swiss part of the station and do not suffer from this inconvenience.
Note that French police in particular has a broad latitude to check ID in many circumstances, not only at the border itself. The details are complicated but it's not uncommon and the official stance seems to be that as long as it's not more than 12 hours in the same spot, it's not systematic and therefore OK from a Schengen point of view.
In summary, I wouldn't put much weight on this “temporary reintroduction” notification either way. And unless you absolutely want to avoid border checks at all costs, there is no reason to be worried about checks having an effect on your train connections. Some kind of check is however always a possibility, Schengen notwithstanding.