Yes, weird features such as "802.11n wifi", "suspending the system when lid closed" etc. Had a well supported older thinkpad (even supports open source bioses etc), and issues cropped up in those areas
For sure, but usually this comes down to "manufacturer picked a slightly cheaper wifi chip with no linux support", "manufacturer is doing weird shit with ACPI they shouldn't", etc.
No. For me, in 16.04 everything was perfect, 18.04 started breaking things