Check around the valve for cuts -- hold the tube under water and check where the bubbles come out. If it's around the valve stem, check the rim for burrs. Especially with Presta valves if you use the retainer nuts. I do -- makes it easier to inflate a tube from scratch, especially with push-on chucks like that on my floor pump (my mini-pumps have threaded chucks).
Recently I forgot to loosen the Presta valve retainer nut after inflating the tube. A few days later it leaked through a nick around the valve stem. Sure nuff, burr around the rim valve stem hole. And I made it worse by overtightening the valve retainer nut. I deburred the rim and reminded myself to loosen the nut after inflating, if I can't force myself to do without the retainer nuts completely.
On the plus side, I'm doing my part to keep my LBS in business during this carumbavirus pandemic (they're limiting the shop to 2 customers at a time, and I wore my mask and tried to avoid touching stuff I didn't plan to actually buy). Had to visit a couplafew days ago so they could pull a jammed crown race for me (they have the proper fancypants Park tool, which I can't justify buying). And they never charge me enough for service favors, so my conscience compels me to buy tubes and stuff I won't need for years. I usually patch tubes until there's more patch than tube, but I don't try to fix tubes with cuts near the valve stem.