You don't need a modded mech. The BSC-27 that you get as a reward from a flashpoint breaks the store if you put it into storage. The store fixes itself if you take it out of storage but then the mech blips out of your mech bay forever.
Glad to know that what I was seeing and dealing with is a known issue. Kept thinking I broke something.
Any chance you have a modded in mech in your storage - that can mess up the stores
I dont mod the game at all. Im not a tech savvy enough for that. Before my injuries maybe, but not anymore