If you wanted to travel between France and Belgium you would inevitably have encountered delays (or worse) in the recent days as a consequence of the sabotage on the French high speed lines. 

Timing of a very local French Railway strike could not have been worse, as the strike today adressed the regular trains on the alternative (non-high-speed) line Kortrijk (B) to Lille (F), via Moeskroen (B) and Tourcoing (F). 

But there is a solution, and if it is not for today, then it will be for another time as it will not be the last strike on the French railways, and trains crossing borders will always be subject to specialties. 

The solution is to take the Belgian train to Komen/Comines, walk 1 km, and continue your journey from the French train station Comines (or vice-versa of course):

Until the 19th century it was one town, but then history happened and the two halves of the city of Comines, on either side of the river Lys (Flemish: Leie) found themselves in different countries. They then became two different cities, with a bridge connecting them right in the middle. The Covid-period here would have been interesting, as the supermarket is on the French side, while most other shops are on the Belgian side. 

Now this community is generally mostly train travel, but train companies do operate buses to and so is the case to Comines, which since a few years is no longer served by trains. Instead the French railways still offer 3 buses per day, and your Interrail Pass can be used on these buses. The bus will only serve the former stations, so it should be a comfortable ride.

If you are not so fond of waiting, you can also spend €1,80 and take the suburban bus (lines L90 and 86) that also bring you to Lille, where rails with trains are waiting for you. There are buses every hour: https://www.ilevia.fr/

Having written all this, I found this website that explains this as well as other border crossings to/from Belgium:
https://www.grenstreinbus.be/busverbinding.php?provincie=-4&id=46 (there is an English version of this website however that one contains less details, so better use a translation of the page in Dutch). This site points out that the suburban lines already have a bus stop in Comines right across the bridge, so no need to walk to the station. Having seen the now defunct station building, personally I believe you should have been there to keep the railway atmosphere, even though you will be taking a bus from there.