You could buy a Bushwhackers Club Membership and have every bit of your Max Energy get added on to whatever you already had during any Level Up while a member.
Or you could plan for a level up and hope to not hit big fruit any time near your anticipated leveling up.
I kind of wish there were an Energy 'drain' that one could waste energy and not get XP but actually not getting 'all' of a level up is what we all have to live with (except members) every time. A small price to pay. Actually it doesn't make sense to want to waste energy just to get some more energy so forget that 'drain' idea.

You should send a copy of the play history showing before thru after your leveling up along with the date/time that your club membership ticket in your Inventory states that your membership will end in a ticket to the Developers because what you say happens is not supposed to happen with a valid membership.
Is your membership up to date?

Well then all I can suggest is that perhaps your membership was not active the time you saw that happen, between memberships...
Or that you might have been mistaken. Some people adamantly believe something, don't see something, don't believe something, until they are told t o check their Play History that shows them wrong. Don't know.

My own membership in the club is minimal. September-March in 3 monthly purchases with perhaps half that time without a membership. I.E. I only join for the CI. And yes, my purchase in the last half of the last day of January ges into the first day of March. Three CI's for the price of 1 even with this years Leap Day.

I'm a BW Club member, and since joining, I've never had a problem with not getting all of the next level's energy added to whatever I have at level-up.