Lots of digital converters have issues with VHS players and their non standard and fluctuating frame rates and sync signals. A more expensive converter may work, but you might be better off just running the scart cable again. You could also use any other analogue input (e.g. the yellow red and white phono sockets) if the scart socket is blocked.
Yes. VHS is a very poor quality PAL composite video source usually, with the signal having a lot of 'wobble' on it (for want of a more technical term). Analogue TV Inputs (and analogue TVs) were designed to cope with this wobble. (Some high end domestic S-VHS VCRs had timebase correctors in them to remove this - and they can often be picked up on eBay - though command a premium)
Modern SCART to HDMI Converters are really more aimed at retro console conversion, and although retro consoles have their own foibles, they are almost always a solid PAL, NTSC or RGB source, so you don't have the 'wobble' issues. To do a decent VHS PAL -> HDMI conversion you will need a converter that does a bit more processing (effectively time base correcting the VHS output).
As others have suggested - if all you want to do is watch a VHS machine output - running it via the RF input (though that will leave it mono and reduce the picture quality a bit) is one solution if you don't want to run a separate cable.
(Incidentally broadcasters have always had to do this with VHS machine outputs - as most broadcast PAL composite kit wants near-perfect PAL sources and has all sorts of problems with the native output of a PAL VCR. Most broadcast operations had a TBC or Synchroniser specifically designed for poor-quality PAL sources like VHS (Often a 'Rogers' box was used ISTR))