External hard drives not recognized

Running disk utility this happens, Running First Aid on "Container disk1" Verifying the startup volume will cause this computer to stop responding. Verifying storage system Using live mode. Performing fsck_apfs-n-X-I/dev/diskOs2 Checking the container superblock. Checking the EFl jumpstart record. Checking the space manager. Checking the space manager free queue trees. Checking the object map. Checking the encryption key structures. Checking volume /dev/rdisk1s1. Checking the APFS volume superblock. Checking the object map. Checking the snapshot metadata tree. Checking the snapshot metadata. Checking snapshot 1 of 12 Checking snapshot 2 of 12 warning: Cross Check : Mismatch between extentref entry reference count (2) and calculated froot entry reference count ((pr extent (278751310 + 1) warning: Cross Check : Mismatch between extentref entry reference count (2) and calculated fsroot entry reference count (1) for extent (655464264 + 1) Checking snapshot 3 of 12 Checking snapshot 4 of 12 warning; Cross Check : Mismatch between extentref entry reference count (2) and calculated fsroot entry reference count (1) for extent (354939587 + 1)