One of the main errors I see people making in solitary practice is over-practicing a single action. Generally this comes in the form of practicing a complex, multi-part action, without the needed external stimulus (meaning an opponent/partner) to give the technique its contextual relevance, timing, and feeling. The negative outcome I have seen, for many, is a type of conditioning that leads to multi-part actions being executed in sparring situations in ways that are non-functional.
Practicing a combination of attacks is only as relevant as the opportunity. For example, training yourself in such a way as to tie a pair of blows together can lead you to wasted actions later when you attack where there is no opening or in a time that is not offered by your opponent. The same outcome can occur with defence and counter-attack pairs as well. If you always train a particular riposte after a given parry, you not only become predictable later, but you may lack the ability to execute a more effective, alternate counter-attack.
When training patterns, make sure you keep your variety high. Practice many different types of follow-on attacks from an initial blow. Practice a wide variety of riposting attacks from a given defence. It is even better to alternate between a few different options in your practice versus practicing a single action repeatedly. Repeat practice can be useful for conditioning your initial motor function, but then varied practice will be more relevant to your ability to be a fluid and dynamic fighter.
Bringing visualization into your combination practice can also add the missing timing component. Imagine a training partner across from you and have your actions respond to their cues. This does require some mental focus but a small amount of this type of practice is far more valuable than a higher amount of rote repetitions of a motor pattern without mental connection.
If you are training to build your strength and power, I recommend that you avoid complicated patterns and instead focus on single or two-movement actions. To challenge your growth, increase the weight of your training tool so that you limit the number of quality reps that you can do to 8-10. Just like in weight-lifting, a smaller number of more challenging reps will pay bigger dividends for power.
Solo practice is an excellent part of a complete training routine. Make sure you train wisely so that the quality of your practice keeps up with the quantity.