TOCs that have taken an excessively cautious approach to training (naming no names in particular!) are now bearing the brunt of those decisions. Some traincrew have retired or left the industry, others have lapsed competency whilst shielding or through the significant reduction in work. Meanwhile, at some TOCs, very few people have been trained to make up for it.
You can't always win though - EMR have been proactive throughout with training, within the restrictions of COVID anyway, and are still up the creek without a paddle at the minute staffing wise.