Over at EK they noticed that their liquid cooling block did not fit anymore on some newer models of the GTX 1080 Ti Strix from ASUS. Since these blocks are in direct contact with the components on the PCB, clearance issues have surfaced. 

As it turned out, ASUS changed the PCB layout of the ROG Strix GTX 1080 Ti. Only certain series of card models seem to be affected, these would be the following serial numbers differ from previous models: HBYVCM064817- HBYVCM999999 and HCYVCM000001- HCYVCM059975. EK also reports that their EK-MLC Phoenix GPU Module FC1080 GTX Ti no longer will fit as well as their EK-FC1080 GTX Ti cooling block. The guys over Tom's Hardware noticed that video cards that have been produced up-to  November this year have not changed/altered (yet).

Should you plan to purchase a water-block for your 1080 Ti STRIX card, please do check out the EK page, they are listing clearly if the block fits or not. 

"Important notice! Due to changes in the PCB design, ASUS ROG Strix GeForce® GTX 1080 Ti graphics cards in the following S/N range are not compatible with EK-MLC GPU Module FC1080 GTX Ti Strix full cover water blocks: HBYVCM064817- HBYVCM999999 HCYVCM000001- HCYVCM059975"

ASUS Silently Altered PCB design GTX 1080 Ti Strix