The Antwerp - Irvine trains appear to have ceased permanently, although it took a while for all the wagons used on this flow to leave the UK, explaining more recent sightings of them. There are still some of the same ICA tanks used on Aberdeen flows, but these are French registered as 877898xxxx numbers compared to the German registered 807898xxxx wagons used on the Antwerp flow. All these wagons appear to be from the same original batch of "silver bullet" wagons, with the country code changing from 87 to 80 at some point.
The last northbound 6S94 was on 25th January. This appears to be the only time it ran this year, with the previous working a month earlier on 21st December.
Here is the final 6S94 at Appleby:
https://www.flickr.com/photos/paulberry59/52648833995/
Most of the wagons returned south on the final 6M74 to Wembley on the evening of 23rd February, and went forward to Dollands Moor as 6B57 the next day.
6B57 is pictured somewhere in the London suburbs (Bickley?) behind 92044 and 66740:
https://www.flickr.com/photos/99279135@N05/52708469672/
Half a dozen defective wagons remained at Irvine, which were eventually made fit to travel and sent as a 6E74 to Doncaster (Down Decoy Yard) on 24th April, via the Tyne Valley.
6E74 is seen here at Haydon Bridge:
https://www.flickr.com/photos/147545292@N02/52845106270/
The following day these six wagons headed to Tonbridge West Yard as 6O57, seen here at St Neots behind 66718:
https://www.flickr.com/photos/d1015/52858625976/
In addition to the six wagons off 6O57, there were 2 more defective wagons already at Tonbridge, giving a total of 8 as listed above. The tanks left for Dollands Moor as 6R71 on 5th June but then returned to Tonbridge as 6Z65 on 8th June for reasons unknown. After receiving whatever attention they were at Tonbridge for, they finally left the UK yesterday, travelling to Dollands Moor as a 6B58 21:01 departure (13th September) then through the tunnel.
VTG liveried 807898074-5 at Tonbridge West Yard on 30th April:
https://www.flickr.com/photos/richardajones/52881042368/
NACCO liveried 807898055-4 at Tonbridge West Yard on 17th June:
https://www.flickr.com/photos/58806173@N08/52983062587/
If there was any plan for these workings to resume in the near future, it seems unlikely that these special workings would have been organised to return the remaining wagons to Europe.
The Antwerp and Aberdeen to Irvine flows ran simultaneously with slightly different products. Apparently the Antwerp service conveyed Kaolin slurry, while the Aberdeen service conveys calcium carbonate slurry.
A link in the description of this drone shot of Irvine sidings explains the difference, with kaolin being a form of aluminium silicate:
https://www.flickr.com/photos/scottdarg/52253069617/
A selection of photos of the sidings at Irvine:
https://www.flickr.com/photos/tags/caledonianpapermill
Blogpost focusing on electric power of these clay tanks on the West Coast Mainline in recent years:
https://leightonlists.com/the-irvine-dollands-moor-china-clays/