Hello, and thanks for the report!
The run log won't be helpful in this case because it's not caused by a serious error.
Instead, to solve this one I need to know your particular loadout at the time, so either have the /user/save.bin file (exit and save/send the file as soon as you see it happening) or possibly even just a screenshot that would enable me to recreate the same loadout and test it.
In the end the game (internally) is always calculating your energy correctly, so if it was going up it should go up. What the HUD shows is only a semi-accurate prediction of what will happen. Obviously we'd like the prediction to be perfectly accurate, but it's somewhat difficult to calculate due to how energy and turns work (independently). In fact, if you were in combat or moving extremely slowly or quickly then you can't even really trust that value because you'll pass many turns (or only fractions of turns) and there may be changes mid-turn that affect the outcome! The value calculation has to make some assumptions, but those assumptions may not always hold true depending the circumstances.
This may not be a bug, after all, but I'd like to see specifically how serious it was in your case and possibly tweak some things if necessary.