1) No unique selling point
Lenovo was not having any differentiating factors in their smartphones. The other Chinese companies started focusing on the single feature to attract the single set of customer segment which want that prominent feature in their smartphones.
Eg:- Oppo started working on the cameras, Mi started working on giving the latest premium technology in the best cheapest price in which other companies are not able to give.
There was no such feature in Lenovo which were not able to make their own identity in the highly competitive smartphone market.
2) No proper integration and utilisation of known
Lenovo made good move by buying the one of the well known smartphone brand, Motorola from Google in around $3 billion. But, they were not able to make it profitable for themselves. Lenovo and Motorola were having similar features and were competing in the same price segment. Later, the company launched a new sub-brand i.e. ZUK which was also competing in the same price segment. The company was not able to give the directions to these brands where as BBK was able to control it's all 4 brands properly in the different price segment with different features.
3) fake types and promises
With the falling reputation in the smartphone market, Lenovo created a fake hype regarding their smartphone Z5, which will be having 4 TB of space with no bezel less smartphone. But, the smartphone was not able to make up to the expectations as it was not having any of those feature whereas was just a normal smartphone. This fake promise took all the trust of the people from the brand, which eventually led to the latest phase of Lenovo in the smartphone market.