1. Middle Management: Middle management at GoCardless tend to be quite young and inexperienced in effectively managing people. Moreover, people are often promoted into middle management positions without displaying real management competency and without adequate training. The net result is that you could easily have your career progression miss-managed and/or have managers who don't understand how to manage people effectively, this is particularly important if you don't fit into the 'typical' mould of a start up employee, e.g. a parent.
2. General Strategy: The company is unlikely to execute its vision of offering the ability to take payments from anyone in any country and in any currency. The regional and operational differences in Direct Debit schemes globally make it virtually impossible to aggregate and integrate each scheme into a single product offered by a single company. Secondly (for several reasons) GoCardless have traditionally struggled to attract the huge companies (think Netflix & Spotify scale) that take recurring payments and would benefit from a global Direct Debit payment network. GoCardless are essentially building a global network which their larger customers will only use to collect funds from say a maximum of 3/4 countries at best.
3. Strategy Execution: The company is in the process of attempting to execute the above and making some mistakes. Primarily becoming extremely bloated, going on a hiring spree (particularly in engineering/product) whilst also aggressively cutting costs. Several hires/positions just don't make sense (e.g. aggressively expanding a marketing department that has yet show it can effectively drive inbound lead traffic), the company is clearly eyeing an exit and in doing so is aggressively cutting its cost base whilst stretching revenue targets into the realm of unrealistic. Startups generally pay a low base, allowing sales people to supplement the base via commissions which are in-turn based on hitting targets. With unrealistic targets linked to pay, the sales team is particularly demoralized.