Can you confirm what version of lede you have installed.
Are you upgrading to 18.06.1 or something else?
I have two devices there were running one of the lede versions, 3rd or 4th from memory , and they upgraded to 18.06.1 fine. (When i upgraded to lede from chaos calmer they both bricked and I had to tftp flash them . )
Can you confirm what version of lede you have installed.
It is hard to say..., because I work with forked repository. It says reboot, but there are some commits from 2017, before 17.01.5 tag in official repository.
Are you upgrading to 18.06.1 or something else?
I compiled from openwrt-18.06 branch so it is ahead of 18.06.1.
What recovery methods does your device have?
I have no idea.
I will try to run the image using tftpboot and will inform about the result.