The CFL (Luxemburg railways) part of the Brussels-Luxemburg line has been switched from 3 kV= to 25 kV~ electrification not so long ago. CFL is now homogeneous 25 kV~, no more dual system tracks in Luxemburg station. The separation between 3 kV= and 25 kV~ is now near the border. Since then, AM96 that were normally assigned to this service cannot go to Luxemburg anymore because they are 3kV= only. Some of those AM96 are effectively 3kV= and 25kV~ capable but there are only 50 of them and they are all assigned on the lines to Lille, so not possible to reallocate enough of them (*). So approximately half of the Brussels-Luxemburg trains are currently made of 3kV= only stock, and therefore limited to Arlon, with a local corresponding move to Luxemburg available, and the other half made of HLE13 + HVI10/I11 stock that can go to Luxemburg. HLE18 is not qualified for CFL yet (it's in progress) so that's why HLE13 are still used. Once HLE18 is qualified, HLE13 usage by SNCB will cease entirely. In the near future, the belgian line 162 will also be switched to 25kV~, I suppose you have noticed the works in progress. First step between Luxemburg border and Hatrival, somewhere half way to Namur. Second step to Namur later, with the electrical separation already visible right near the bridge over the Meuse river.
(*) this might change next year: there are currently tests in progress with SNCF AGC bi-bi carts equipped with belgian TBL1+ safety system, on the line between Lille and Tournai. Probably those will take over between Lille and Tournai as of the next end of year schedule change, and this would free up enough bicourant AM96 sets to serve the Brussels-Luxemburg service. AGCs will use the 25 kV~ catenary and switch to diesel when the wires are 3kV=, as they can't take that. Not sure where the switch between electric and diesel mode will take place though, as the separation between 3kV= and 25kV~ is not at the physical border. SNCF rules have this kind of mode switch foreseen, with supporting signals along the tracks for it, but there is nothing foreseen in the SNCB rulebook for that...
Namur station works are complete regarding trackwork (although I do not understand why the entry/exit from/to Liege (line 125) is still so slow) but final works on the building have long be waiting for a decision about what to do with its roof. In the beginning, a movie theatre complex was foreseen, but this didn't go through. Now it's been decided to build a bus station on this roof, works are in progress.
Line 161 quadrupling (RER project) was stalled for more than 5 years because of lack of funding. Now the funding issue has been solved and works are in progress again. As it is not possible to disturb or detour the existing traffic, the layout of new tracks will have to be carefully planned (two tracks must remain available at all times, except during nights and week-ends) and are likely to take several years. Works on quadrupling the northern part of line 124 Brussels-Charleroi have resumed as well.