I observed the same on my Tolino Shine 5. I contacted the seller of the device with a longer list of software bugs. They responded to that list, for some of them (e.g. Missing sentences at chapter ends), they mentioned that these issues would be "known to the software developers and a fix is work in progress". For incorrect letter spacing, they mentioned that they "relayed that feedback to the developers".
I'd suggest others do the same - I guess they are unlikely to fix that issue if I'm the only one complaining
.