If I earn units when the units backend thingy is down (displaying units as '0' basically), will they add up later? Or will I just lose them because I earned them when the backend was down?

[Heavysteam]

The developers have made the game able to remember how much exp and what achievements you have earned while the backend servers are down.

@macdguy

Updated client system to handle backend downtime better (queuing up achievements and exp so you’ll never lose track of them when the backend goes down)

Hot Fix 0.7.0.3

This update addresses several issues that were reported. All unit transactions have been moved to the new backend which should make everything a lot more stable now. New Payout System We’ve reworked the payout system to use the new backend, ensuring you’ll be getting payouts for all games properly from now on. This change also should see faster connections to the new backend. New Store Buy and Sell System With this change we also reduced store transaction errors and made the store transaction…

Most likely said system is also able to remember how many units you have earned and then promptly give them to you once the connection to the backend servers have been re-established.
Also due to the fact that achievements give out units when completed, it would be weird for said system not to remember earned units.