Hi Kaiserquill,
Axolotls do have the ability to jump quite a distance, thus the need for a secure tank lid/ mesh netting to prevent them from jumping out of the tank onto the floor.
There are several reasons why an axie might struggle out of the water. I will list some of the main causes and what you should do to prevent/resolve the problem.
1 - Water parameters - Should have ideally 0 ammonia, nitrites and <60 nitrates. pH ideally around 7 although a range of 6.5-8 is tolerable. Invest in a good colourimetric solution type test kit and test your water parameters regularly. Perform regular 20% water changes with clean declorinated water. A good filter will help substantially. Remove uneaten food and detritus.
2 - Water temperature - High temperatures above 22 degree celsius, especially for a prolonged period. Cool the tank down to a comfortable stable range of 16-18 degree celsius.
http://www.caudata.org/cc/articles/cooling.shtml
3 - Aggressive tankmates. Axolotls should only be kept with other axolotls of a similar size. Small feeder fish after minimum 30 day quarantine is also ok. Even with axolotls, some axies are more aggressive (such as wildtypes) and can cause other axies to be traumatised and hence struggle to get out. Monitor for aggressive behaviour. Separate axies or use tank divider.
4 - Parasites. Some types of ectoparasites notably flukes and anchorworms can cause severe skin and gill trauma to axies, causing immense discomfort. Axies would become frantic and writhe to relieve its discomfort. Refer to a vet if suspected.
5 - Excessive vibrations and light. Excessive noise, heavy footsteps (ie running kids) and intermittent bright light exposure can all startle axies. Position tank in a dim, cool, quiet area of the house with minimal interference from household appliance or human/pet traffic. Provide minimum of 2 hiding places per axie.
6 - Spontaneous morph (rare). Axolotls morphing into the terrestrial form will undergo apparent physical changes and would want to leave the water. Provide a floating platform such as a turtle island just in case. Morphed axies will require a vivarium setup and can no longer be fully aquatic.
Cheers.