This problem is caused by the recovery ramdisk compression method. In new twrp builds for this device we usually use LZMA but that isn't currently supported by CarbonROM's sony init. You can not do much yourself, except using an old TWRP with gzip compression or wait until https://review.lineageos.org/c/LineageOS/android_device_sony_common/+/252923 is getting merged into carbonrom.
Thanks for your answer.
Reading more carefully your post, I realise you had already explained that, but I hadn't read the "Additional information about the recovery on this device:" part, sorry. You've saved me from a headache because of my lazy reading.
For the moment I'll use a recovery which doesn't compress the ramdisk with LZMA, this one, which works perfectly in my device, but it'd be great the patch for LZMA was getting merge into CarbonROM to use new twrp builds.
Thank you very much.