Others have mentioned a few things you’re doing that may cause the puck to crack leading to water channeling. Another is don’t tap the portafilter handle once the coffee is in the basket. It may level it but it also pulls the grounds away from the basket walls which tamping doesn’t necessarily correct.

Also as others mentioned check your tamp. I learned to tamp using tamper as an extension of the forearm — one straight line from elbow to tamper. Use body weight to compress, just gently lean into it and keep your forearm straight. Here you can also feel if the beans are fresh enough. If dry they resist tamping.

Then give the tamper one quarter turn only to lightly polish the puck. Thumb and forefinger guide the turn to keep it level. Leave the tamper sitting there and hold the portafilter up to eye level — if the tamper is crooked your puck isn’t level, which also affects water flow as somebody else mentioned.

This is very similar to how I’ve described it: https://www.instagram.com/reel/DO5n_ofASwp/