I would like to make a speculation on how the current BG game mechanics may be.
(if TLDR, then refer directly to the blue-colored statements at the bottom for a shorter version).
Because the 'investment' is not banked in until you finish a BG, I suspect there is not one but TWO (!) resource banks are used.
The 1st resource bank is used for payout, i.e. you get paid out based on the amount of resources in it.
The 2nd resource bank is used for storage of resources, before they are transfered to the 1st resource bank.
Game mechanics/logic:
1. As long as a BG is not finished, all 'investment' will go to resource bank #2 for storage.
2. If a BG is finished, all resources stored in resource bank #2 will be transferred to resource bank #1.
3. Payout for the BG just finished will be referred to resource bank #1. If it is empty or not enough, there will be little to no payout.
4. Say a level 20 BG is halfway done, the resource bank #2 is stored the 'invested' resources. The resource bank #1 is empty.
5. Now the level 20 BG is finished, the resource bank #1 is referred for payout. No payout is made as there is no resource.
6. As a BG is just finished, all resources initially stored in the resource bank #2 before the BG was finished, is now transferred to resource bank #1.
7. Player feel frustrated there is no payout for this level 20 BG. He attempts level 40 BG. All resources he puts in before finishing this level 40 BG are stored in resource bank #2.
7 (a). Now the player finishes this level 40 BG, first the system refers to the resource bank #1 for payout. Resource bank #1 has only resources transferred from resource bank #2 from finishing level 20 BG. So the BG pays according to the amount of 'invested' resources successfully transferred from resource bank #2. Recent 'investment' from finishing the recent level 40 BG is excluded. Player feels shortchanged in payout because he got a level 20 worth of payout for finishing a level 40 BG.
7 (b). After the payout is done, the system now transfers all the resources ('invested' in level 40 BG) stored in the resource bank #2 to resource bank #1. The transfer is allowed because a BG is just finished. If the level 40 BG is not finished, the transfer will not take place. If this happens, the resource bank #1 will be empty and the next BG finished will have little to no payout, but the resource bank #2 will accumulate more 'investment'.
8. The player now do a level 30 BG and finishes it in one go.
8 (a). The system refers to resource bank #1 for payout. There is resources in it from the transferred 'investment' from doing BG level 40 previously. So the player got a level 40 worth of payout for finishing a level 30 BG, He feels elated at the big reward.
8 (b). All the resources 'invested' in finishing the level 30 BG are now stored in resource bank #2.
8 (c). After the payout, the system checks to see if any new BG is finished. Yes, there is (level 30 BG just finished). So all the 'investment' stored in the resource bank #2 is now transferred to resource bank #1.
I hope this is not too confusing, but generally...
Ingredients needed:
1. Resource bank #1.
2. Resource bank #2.
3. 'Investment' of resources by player.
Steps involved:
1. System refers to resource bank #1 for payout first. No resource, no payout.
2. 'Investment' of resources is then stored in resource bank #2.
3. If a BG is finished (regardless of the level), the stored 'investment' in resource bank #2 will be transferred to resource bank #1. Or else, the 'investment' stays stored in resource bank #2 and accumulate until a BG is finished, before a transfer is allowed.
The result from all these is a payout lag of 1 BG. Assuming my speculation is correct, this lag can be rid off by finishing a very low level BG to trigger a transfer.