Those plants look healthy, and it's normal to lose a few leaves after a repot. Look up plant edema and see if you think that may be going on. I use a chunky mix also but still get that on some leaves periodically. Fluctuations in temp outside are impossible to control, and a lot of them are out where they get rained on. I remove those leaves and don't become alarmed unless leaves are being lost at a rapid rate (or there just aren't many to spare to begin with.)

Perhaps Petasites japonicus var. giganteus.

Looks a bit like Ageratina altissima 'Chocolate' aka Eupatorium rugosum

I think your initial hunch is correct. Based on the ratio of potting soil to peat, I would guess that your soil is a bit too water retentive. Peat tends to hold lots of moisture. There are some much better soil mixes recommended on this forum, but perhaps in the meantime you could try 1/2 regular potting mix and 1/2 perlite. You'll get faster drainage, and you'll be able to flush the soil with a large amount of water in order to remove salt buildup without the concern about over-watering. Watering twice a week lightly is a recipe for problems. **Keep in mind that you'll need to change this soil out probably annually, as run-of-the-mill potting soil can compact over time like cement (personal experience). You can keep the same pot as long as there are drain holes. Tilt the pot each time you water to remove any excess water. This style of pot is prone to puddling near the drain holes, and while attractive looking, I am not a huge fan. I'm no anthurium expert, either, but you might want to do a search to find out whether you should water when soil is completely dry or maybe a several inches down. Many tropical plants, like peace lilies, can wilt from lack of water and bounce back immediately with no ill effects . Over-watering is usually the killer.When you re-pot, take a look at the roots. If they are mushy and smelly, you've got rot. Sometimes you can cut off the rotted sections and start anew, but other times, you just have to toss the plant. Sorry for the length, and good luck. I'll close giving many props to Al (tapla) on this forum who taught us all about the basics of good soil drainage. Check out his posts when you have a chance. He's way smarter than me. : )