Do you use a touch screen, controller, or pc for gameplay? I used to have this problem when I used a touch screen, so I assume this is what you use. This is because if you misplace a block, it often doesn’t register that a player is in the blocks way, and it still places it (causing you to be pushed out of the way and fall). To avoid this glitch, you can switch to split controls, which will make it easier to speed bridge and lower the risk of misplacing blocks.
Otherwise, I might suggest investing in a controller that is able to pair with your device. Not only would you be able to jump speed bridge then, but it would practically make the fall risk a 0 percent chance.
If you are falling and not using a touch screen, there should be a way to prevent this, because bridging on pc’s and with controllers doesn’t seem to ever have this problem. However, if this is the case, try contacting a player that uses a pc or controller and ask them how they bridge.
As for the extreme variation in knock back, it usually depends on the player’s connection to the server. If you come across a player with delayed or even no knock back at all, they may have a poor connection.
Lastly, the iron axe isn’t a weapon worth buying; It certainly isn’t worth 40 diamonds (unless you reach an endgame). Also, I think the axe isn’t the best weapon (rather the iron sword) for bedrock players. buy a good gold sword or the iron sword, bread, and maybe some armor instead of pouring it all into a weapon
Hopefully this helps you