The things I tried were: Restarting the game and killing the boss, re-enabling the mod, reinstalling the mod; disable some mods that could cause it to glitch after an update, like calamity, spirit mod, alchemistNPC and joost, didn't try doing that with furniture, foods and fun and thorium because disabling either of them crashed terraria.Does it still happen after closing and re-opening Terraria? If not, you might need to re-kill the boss. I had a problem where I killed a boss but the game didn't detect it. That might be your problem.
I'm thinking about clean installing terraria again after I'm done with my thrower playthrough.
I tried to see with another character that beat supreme calamitas and the summons are all there except for the pre hardmode one, when I got back to my thrower it was showing only the post moon lord shop, I had to go back to the other character and change to pre hardmode shop.
I'm uploading some screenshots of the the shop with boss checklist, I did try to kill the pre hardmode bosses up to the point I am(after restarting terraria) to see if it was going to change anything but it still didn't work.