Didi2000 Level 2

Hello My build a bot boosters have suddenly disappeared. They were fully charged and I haven't lost a level. Just gone back to no booster level on both my devices when I logged on this morning. This is very frustrating, as I am approaching a sequence of hard levels and I will need them. Can you please advise?

Thanks, @Crimson_Dawn. Actually it's not the first time it's happened to me, but I thought it was a glitch. Good to know if it is just part of the landscape we're finding our way through!

Thanks for your answer, Sukanta. I wasn't aware of this rule, and thought it was glitch in the program. The first time it occurs is level 4598. As I noted, when I first passed 4596 and 4597 the boosters were available (I needed them to pass) and then they disappeared. They're available on level 4599 but then not on 4600…