Thanks both!
So you think the cause of the problem is not related to the Weight of my blocks.
I did repair my wallet and, even though my mac should automatically sync the time with the network, it appears my clock was way off.

`$ sudo ntpdate -u time.euro.apple.com
22 Jan 11:44:40 ntpdate[48904]: step time server 17.253.54.125 offset -58.859095 sec
`
I'll try modifying /etc/ntp.conf to specify shorter minpool and maxpool, hopefully that will sync my clock more often.
Guess I'll have to wait and see if any new minted blocks get accepted.