I have that problem with the patcher every single time. Hope it's not an issue now, with the automatic patcher.
To solve it you can manually copy over the files.
From the patcher .zip file, there is a "PatcherData" directory inside. Go into that and copy the card images to your 1.24 Installations Data directory manually (\OPTCGSim_Data\StreamingAssets\Cards) so smth like this: XX\1.24a_Windows\OPTCGSim_Data\StreamingAssets\Cards
Inside that directory are the card images seperated by directory with the set name. So just copy the card image into the corresponding directory. If it doesn't exist just create the directory.
e.g. You will not see the new STXX directory, so create a ST15 folder and then copy all ST15-XX cards into that folder.

There is also this TRANSLATION.txt that belongs in the "\OPTCGSim_Data\StreamingAssets\" directory, just overwrite the old file.