I think kernel 4.14.206 was available since 5.1.4:
Nov 5 20:40:02 gw updater[7311]: repository.lua.lua:50 (Globals): Target Turris OS: 5.1.2
Nov 5 23:10:46 gw updater[18561]: repository.lua.lua:50 (Globals): Target Turris OS: 5.1.3
Nov 5 23:10:51 gw updater[18561]: updater.lua:94 (Globals): Queue install of kernel/core/4.14.202-1-8b9af84bd92487dbe3b82318bc09b670
Nov 8 21:24:57 turris updater[17470]: repository.lua.lua:50 (Globals): Target Turris OS: 5.1.3
Nov 17 17:08:58 turris updater[14342]: repository.lua.lua:50 (Globals): Target Turris OS: 5.1.4
Nov 17 17:09:03 turris updater[14342]: updater.lua:94 (Globals): Queue install of kernel/core/4.14.206-1-8b9af84bd92487dbe3b82318bc09b670
are you sure there are updates for kernel package?
I have noticed TOS tried to reinstall multiple packages in 5.1.3
maybe you have the same issue?