Hardware that forwards packets usually forwards IP packets, it doesn't care about TCP checksums and doesn't recalculate them. TCP stack in your OS is the one that does that.
It has to be a special kind of hardware that does much deeper packet inspection (DPI) to recalculate TCP checksums, usually used for spying, throttling, censorship, injecting ads, injecting exploits, etc., but not merely routing/forwarding packets.
Switches (L2 devices) recalculate Ethernet CRCs (L2 error detection codes), and routers tend to calculate TCP/UDP checksums (L3 error detection codes) and everything below. I've seen exactly this issue with switches that have bad RAM before, and I assume that they just have a router with bad RAM (and without ECC RAM, which looks embarrassing).
It has to be a special kind of hardware that does much deeper packet inspection (DPI) to recalculate TCP checksums, usually used for spying, throttling, censorship, injecting ads, injecting exploits, etc., but not merely routing/forwarding packets.